As a bowser main i can tell you he is NOT the best he loses to any half competent zoner/projectile spammer. His smashes are suppose to have armor, never feels like it. His side B can literally be controlled by your opponent to make you lose a advantageous stock.
his saving grace is he’s fast and he’s very heavy. Thats about it.
lets look at krool, super heavy, has a crown boomerang (heavy armor ability), cannon ball (zones and kos),vaccume (a bowser jumps over a cannonball only to sucked into his gun) has life saving body armor, insane recovery, a down throw/down tilt kill confirms at low % and a counter...
But then theres samus... i need not say more on this topic.
bowser can be good sure but he’s ill-equipped to deal with most of the ssbu roster.
Clearly someone did not do their research.
First of all, I'll say what you got wrong. His smashes do have damage-based heavy armor-down smash and up smash can take 10% and fsmash can take 12%. It only works on certain frames, but it's still amazing if a bit situational.
Side b can be controlled by your opponent, but it depends on the percentages. If your opponent is up and you're down in percents, they can't do as much. Whoever has the least percent gets the most control-at least, from what I've heard.
And, Bowser has so,
so much more than "fast and very heavy."
Bowser has an amazing MU spread, no matchup is unwinnable, relatively frustrating at worst, EZ at best.
His combo game is simple yet brutal, dealing 40% off of a single up throw -> nair. Landing fair leads into dash grab among other things like up b and tech situations. Up tilt is also good for mixups and occasionally combos. Nair is his greatest combo tool by far, leading into basically any aerial move at many percents, as well as ftilt with the early back hit. This means Bowser has a very low % kill confirm on most characters. Jab can lead into dashgrab and also is good for jab lock -> dsmash. Up air is a very good combo starter on big characters.
Bowser can seamlessly edgeguard with down tilt and forward tilt, not to mention neutral b (invalidates nearly every recovery), runoff fair, runoff dair, runoff uair etc. Not to mention his side b which is amazing for suicide kills if used correctly.
He has some of the best ledgetrapping in the game. Holding shield lets you get a big punish on most anything. Up tilt at a certain spot covers every option (except character specific ones like jump -> counter). Buffered SH dair can kill your opponent early if they jump and it also covers getup attack and neutral getup. Down b catches hanging opponents and either spikes them or sets them up for a true back air follow up. Fair is very good at catching ledge jump as is up smash.
His kill potential needs no introduction. Damage based armor on every smash and tilt means you can pull one off if you think your opponent will attack you with a weak move. His grab range is freaking incredible (especially pivot grab) and fthrow and bthrow are really good kill options. All of his aerials are amazing at killing. All tilts are amazing at killing. All smashes are amazing at killing. Heck, even his JAB kills fairly early. Needless to say, as long as you're not rushing in and spamming mindlessly (which you shouldn't, as Bowser is a bait-and-punish character) you will have no problem closing out stocks.
Fire breath deals 40% max charge on average, if you get the closest hit first. Also works well for camping and aforementioned edgeguarding. Flying slam, while it can be altered by the opponent, is hardly ever an issue if you know how the move works. Kills incredibly early, and if they don't know how to DI it you can kill them off the top platform ridiculously early. Also can combo out of nair, meaning you can do that for a kill confirm. Down b is a move that is bad if you don't know how to use it well, but amazing if you do. Breaks shields at nearly full health, does crazy damage and knockback, can cover the majority of ledge options, and it can spike. Up b is a frame 6 get out of shield option, making it one of his best tools for playing the patience game. The recovery is good if you know you can mash B after the initial boost to gain much more height. Up B is also great for rushing into your opponent (generally it's better to not rush in, but do it if you feel the need to).
He has one of, if not, the best advantage game of the roster. As soon as the Bowser player gets a hit, and they know how to punish your options, there's a good chance you lose your stock to a Bowser string. If you're in the air, he has many tools to deal with that-up tilt and up smash are great. Double jump up air, I believe, is unreactable (up air is frame 9). If you're offstage, you better mix up your recovery as best as you can, because if he decides to runoff or fire breath, you're toast (no pun intended). On the ledge, you need to utilize character-specific options or do something completely unexpected, or you're toast. It will take lots of practice to get this good with his advantage state, and even I haven't exactly cracked its full potential yet. But I have played Bowser for well over a year now, so I've done really well in his advantage state.
This is not to say Bowser is invincible, not at all. While his kit itself is extremely good and one of the best standalone kits in the game in my opinion, his weaknesses lie in his character itself. He's combo food, and offstage he doesn't fare too well. His roll and techroll data are absolute s***, his directional airdodge doesn't exactly go far, down tilt and up b have inconsistent hitboxes, etc. Projectiles, though, aren't that much of a problem for Bowser, because he can jump over them, fastfall, and go on with his day. He doesn't automatically lose to zoners and combo characters, even if Young Link and Greninja, his worst MUs, can be a pain to fight, they're nowhere near impossible to beat. He's extremely well equipped to deal with most every character.
If you don't believe what I said above (or don't care for reading it) then take a look at his results. LeoN alone is top 30 PGR, and there's no other superheavy solo mains I can think of that are above him.
K. Rool is my secondary, and while I don't know him nearly as well as I know Bowser, I'm not blind to the fact that he's a low-mid tier at best.
Bowser's heavier, you kind of contradict yourself there.
has a crown boomerang (heavy armor ability)
The move is quite good, I will say, and one of the better things he has.
cannon ball (zones and kos)
It's an okay move, but the startup and endlag is atrocious.
vaccume (a bowser jumps over a cannonball only to sucked into his gun)
If a Bowser jumped over the canonball, wouldn't he just down air?
Depends on your definition of "insane." If all you want in a recovery is sheer height and a hitbox, then good on you. But when recovering anywhere that isn't below the ledge, you can take advantage of him easily, since the hitbox is only on the top of him and it goes incredibly high and falls pretty slowly, meaning if Rool is recovering from the far right middle, he's dead. Landing lag is trash.
has life saving body armor
Belly armor is insane, but it also acts as a second way to get your shield broken. Needless to say, and in the words of a great hedgehog, "That's no good." Not to say his belly armor is bad, it's awesome, but it has a major downside.
a down throw/down tilt kill confirms at low %
I'm sorry, what? As far as I know, down throw kills at like 120% on most characters with good mashing. Down tilt is better but still, if you have any clip of getting a kill confirm at low % off of any of these moves please show me, I've never seen it been done before.
The counter only covers the front of him, not the bottom, top, or back, so it's very situational relative to nearly any other counter in the game. It's good, but nothing to write home about. It also has awful endlag, meaning that if you're playing ping pong with someone with a faster reflector, or just miss a counter, you're getting hit.
K. Rool has some great things about him but ultimately its not enough to save his character. He's slow, many of his moves have considerable endlag, he can't zone all that well despite having two projectiles, his main gimmick is also his downfall when overused, recovery is awful, and he just doesn't have a great matchup spread, despite what some Rool mains might tell you. While at least all of Bowser's matchups are winnable, K. Rool's worst matchups are less so. Recently, Roolcord (the King K. Rool discord) had a crew battle with Linkcord and didn't take a single stock. So no, K. Rool is far from the best heavy and arguably the worst, though Dedede and DK aren't amazing either.
TL;DR Bowser is amazing, K. Rool is not nearly as good.