Let's talk about Bowser and Donkey Kong. Dabuz puts both in -3. If this is the case (and I, frankly, don't find it too implausible), then my assessment of Donkey Kong and Bowser is correct, and they're not top 25. Bowser and DK have both done much more as counter-pick characters rather than solo characters, but counter-pick potential isn't really relevant when it comes to tier lists. People see Bowser and DK do incredible things with their kill throws, but let's not forget that these characters have some pretty bad MU vs several top tiers and high tiers (-2 and potentially even -3 MUs), making them not really solo viable and not that great. Toon Link, Greninja, Mega Man, and Villager have much better solo potential than DK and Bowser. At least they can land (to some extent).
I'm not necessarily disagreeing with your thoughts, but keep in mind that, more often than enough, a matchup chart projects what each matchup SHOULD turn out, and not how it WILL turn out. Reminder that HIKARU's first appearance overseas earned him a win against, surprise surprise, Falln, and 2-0 even, if that wasn't proof enough of how easy you can choke this matchup.
More on that: The extremely strong advantage state of the grappler characters, and to an extent, other characters like Ryu, makes them capable of applying much more pressure out of nothing than other characters. With that in mind, the opposing player may be seeking the safest options out there, often trading any kind of diverse play. But these players are not A.Is, they're bound to come out of their shell of safety & commit to something once they feel like they've conditioned their opponent enough into making something dumb just to get out of that state. With that somewhat respectable strategy on paper that's applied by many players comes one major flaw: You just potentially gave them what they want. This widespread strategy would often require enough time that your camping of any kind could get busted by these far from optionless characters ( Ryu's shield pressure, Bowser's command grab, DK's decent fall speed for empty hop purposes and fantastic Bair for poking purposes ), or being quite patient, which very few players are in the current state of Smash 4. Thus, you're kind of just hoping what you've done will suffice to get in an advantageous position where these characters will indeed suck, but are once again not optionless. Even for the best of the best characters at f*cking up the heavies can't guarantee taking their stocks, far from it.
That's just an example of a situation where your eyes may be thinking that the grapplers are going through a situation about as hopeless as platform camping Little Mac when at Low to Mid%, but it may not be the case and this is all part of neutral play that could turn out as good for one than the other, as one sided as it may sound in the first place. This kind of situation just reinforce how easy it is to choke the grappler matchup. They SHOULD be getting f*cked up, but it's still entirely up to you. Since these situations are more common for them than for your character, they also have more knowledge of all the baits they could be using against you. In a way, you're engaging in a terrain that, despite being the weakest area of your opponent, they should have mastered far more than you, if they do want to beat players like you. There's a lot of these cases in Smash 4: The " This is free vs This could be a huge pain in the a*s to deal with " where players on the 1st category will mainly practice their advantage state, while the others will practice everything. That's why Meta Knight loses so much to floaties.
Anyway, all of this exemplified talk leads me into saying that: It's unarguable that the heavies have some less than ideal matchups, more than the characters you'd expect to see around where they are on most tier lists. However, with the sheer amount of pressure they apply by virtue of their insanely rewarding moves, they're more likely to clutch out these bad matchups than anyone else on the cast. I think the same could be applied to Ryu, Falcon, Luigi, and to an extent, Meta Knight. These are more likely to beat a good player of their worst matchup than Pit is, despite Pit's worst matchup probably being better ( Bowser/DK in mind ) or as bad ( The rest of the characters listed ) as them.
Tl;Dr You're bound to do what the grappler wants you to do to some extent, and if you're playing the whole patience game wrong, you might have given the grappler the tools to bait you into a commitment that will get him his rewards. Grapplers are almost by definition the characters that can clutch bad matchups the most, along with other characters with extremely strong advantage states. While they could be " figured out " and suffer a huge drop in results, i don't think this is the case for DK or Bowser. Not enough players have reached a level of confidence to overwhelm the heavies & render them inefficient. I think that MKLeo's, currently a contender for best player in the world, multiple losses against heavies is a testament to that ( Although he's getting better at it )
I remember that! It definitely proves that he is in it with the "Mario is not good" meme. 
