The philosophy of banning items is very interesting to me because you have to try really, really hard to make your explanation not just boil down to "cause we don't like them". I'd really like to see what you come up with.
Yeah, like, that's the thing. The original ban in Melee happened long enough ago that I wouldn't be surprised if that actually was the reason why they were banned at first. But I think now, with a better understanding of the design philosophy behind Smash, how competitive Smash works, and items' impact on gameplay, I think it might be possible to work backwards and figure out a good reason to
keep them legal across iterations.
Typically the most consistent argument against items is the RNG element that is introduced into the game. Although some items are tame, others such as the Gust Bellows and Master Ball are obscenely good at killing people at 0%.
It isn't interesting or fun when a Master Ball spawns in front of the opponent because that potentially could be the loss of a stock for no reason other than "because the RNG Goddess willed it".
Conversely when I've played with items I've had capsules with bombs in them spawn in front of my attacks, and even food spawn on top of me while trying to perform a wake up attack (Zelda ate the cake while laying on the ground and got fsmashed by Ike, I tell you what, I was not happy).
Ultimately one of the biggest reasons I guess is that you simply cannot plan or prepare ahead when items are in the game and 70% of the time the game degenerates into "capture the hill" where you chain item combos together to keep the opponent offstage or dead, turning the game into a battle of items rather than characters.
That's the argument I've seen the most, and I think that only scratches the surface. For the thing with some items being obscenely good at killing at 0%, or with items sometimes interfering with your ability to perform a basic attack, I was once asked "why don't you just ban the problematic items" and there really wasn't much I could say in response aside from "pretty much every item is degenerate in some way or another." Over the past couple of years, I've started to realize that talking about the problems with individual items misses the forest for the trees. It overlooks the fact that the problem isn't just because of items individually, it's because of items as a whole.
This is an idea I've been turning over in my head for years now, and one I'll probably be coming back to and tweaking quite a bit for years to come as my understanding of Smash improves. I can explain in the abstract that items generally have a net-negative effect on the health of the meta, but I have a hard time giving concrete answers as to why - though anecdotes like yours are certainly helpful. What I have in mind - which I pretty much outlined in the final paragraph of my previous post - is built on two ideas.
First, that the main goal of a tournament is to comparatively measure its entrants' skill at an activity - in layman's terms, to determine, roughly, who's the most skilled at something, and who's more skilled than who. The main goal of a ruleset for a tournament is to outline how the skill will be tested. There are many factors that go into designing one, though the one we'll be focusing on here is the need to keep the metagame relatively healthy, and the need to ensure the results are valid.
Second, there's the idea of a game's skill floor and skill ceiling - the basic level of competency needed to engage with it in any meaningful way, and the point where you're so good at the game that any improvements won't make any difference. The lower either of these is, the easier it is to reach that point, and the higher they are, the harder it is to reach. These are also independent of each other - raising or lowering one won't necessarily raise or lower the other, and it's possible to raise one while lowering the other.
Items, by their very design, create an environment where factors outside of either player's control can have a larger impact on the results of the match than player skill. While there is skill to be had in effectively utilizing items, they act as such a strong centralizing force that they invalidate a lot of the other skills that go into the game. Playing with items enabled may raise the skill floor compared to playing with them disabled, but it also
lowers the skill ceiling by a far greater degree, making the game more shallow overall.