The thing about Bowser is he just doesn't have many good options, a good move set, or good movement. He's slow, his weight makes him combo food, he is a huge target, and he has very linear recovery. You don't have to beat a good Bowser to understand that. On the other hand, Sheik doesn't have these problems so it wouldn't make sense to rate her that low.
Sveet losing to DJ Nintendo really just speaks to differences in skill level, and I'm not sure what that has to do with tier lists.
I totally agree with both of you. Kirby and Bowser are very limited (Bowser far more). But the main point is that how can you call a character garbage and then get beat by them, the skill gap is not that large either (especially in the case of ORLY and Triple R, they are even. DJN Bowser to Sveet's top tiers the MU gap would still put the favor heavily on Sveet's side). That pretty much already qualifies them as not "garbage" and also seeing results against other top tier respectable players that disagree completely with the "Kirby is garbage" sentiment. Most smashers that have never faced a "good" Kirby think it will be a piece of cake and lol at the fact that there are "good Kirbys", they usually get massacred. Those that know the match-up and have played against a Kirby usually hate the match up because they know it's actually kind of frustrating and more difficult than what the tier list would suggest (can duck attacks and grabs, Fair is pretty annoying and hard to counter, grab range is actually good, kirbycides, Tilts can space well, Dsmash has a dangerous KB angle and has reach, Up Air is very powerful, Dair can be weird to meteor cancel, etc)
And if personal experience and tournament experience has nothing to do with giving an opinion on a tier list then why does Sveet ask for credentials. Why don't we all just sit and talk about hypothetical imaginary match ups, experience doesn't matter? ummm... okay
The other main point was to correct both Varist and Sveet who were obviously misinformed about Kirby's options and approaches and clearly had no experience themselves with the character even at an entry level. Many of us corrected them outright.
For Kirby specifically I've never seen a competent Kirby get destroyed and in the case of Mooninite, Triple R and others (Malkasaur and C.Rabbit) they've been able to hold their own and win over top tiers from equally skilled players. Even Bizarro Flame and Mew2King who far exceed their skill level and use MUCH more viable characters....and in those sets concerning Triple R he SD'ed a few times and wasn't even playing at his fullest (probably nerves), yet he still kept it very close. With other characters that are above Kirby you can routinely see them get demolished and gimped in 10-15 seconds even in the hands of their top mains.
So again not "garbage", the main point.
You can't really gimp or kill a Kirby since his recovery while most will blab about being bad will still keep him alive much past other 0-death combos and ledge guards on Fox, Falco, Falcon, Ganondorf, etc. This combined with his weight and floatiness can make him hard to combo to death fast, he's easy to kill fast once above 70-100, but you have to land a KO move not many guaranteed combos into kills at high percents.
Sample size is also a huge factor. Kirby has MUCH MUCH MUCH less representation than the top tiers. This can be argued either way and that his placement feeds into the lack of mains, but it's still a large factor in discussing him. Scientifically you don't ask one person a question and then publish your results on the behalf of a large population. Yoshi has way more potential than Kirby, but just as an example of sample size no one was using the character seriously for a LONG time at nationals until AmSa took 5th at APEX 2015. Even then it's one person, the chances of just one person being that amazing to propel such a forgotten underrated character are exponentially less than the sea of 10s of thousands Fox/Falco, Sheik Mains out there who can't even place at nationals.