Chesstiger2612
Smash Lord
I think a big proportion of the community will think their inability to play aggressive makes them weak, and that will have the effect of underrating the ICs, especially in "Community Tier Lists", tier lists made by people not wary of this and in worst case also the PMDT. In fact, there is a correlation between being able to switch between multiple game paces and the characters strength, but that doesn't lead to any causality for the individual case which is determined by far more factors.The difference is that those characters are probably good enough, that those campy options are an additional luxury, instead of the "optimal' playstyle you would probably have to conform with to keep up. Fox gets to win MU's without lasers, Sheik can grab a few people for free, etc. Factoring in the highest absolute level of play, where a person is willing to play PM IC's as lame as possible, it still doesn't paint a strong picture for the character. A player lack of willingness to play that way isn't a reason for thinking they are bad; it may shine a light onto other problems though. Questions like "Is a character limited towards playing this way?"
IC's don't have variables that matter enough: they have plenty of knick-knacks and different tools, but the nature of that character lends to situations where you can't mesh together those tools or strongly "wedge" the advantage you might get from a choice.
Your last points are somewhat true. There are many situations where the huge pool of options doesn't help that much, which will probably be reasoned by the ICs characteristics, so them being not able to deal with this and therefore having a weakness there. But this is only part of the reason. Some of these bad situations could be avoided before, ICs do have the tendency one bad decision puts them in an uncmfortable situation for a longer time / until more inaccuracies from the opponent happen. This isn't such a big factor when the IC player doesn't do these kinds of "no punish but long-term-harming" neutral game mistakes, for example something ending up in losing space while keeping up the defensive structure, this will more likely result in situations where there is no retreat and even guaranteed or high-probability punishes for your opponent. Some of the situations where they fall short are also dued do the character, no doubt.
Not trying to say they are top tier or anything, but seeing them in so many bottom 3s / bottom 5s is something I disagree with. By the way, I appreciate the constructive discussion