I'll seperate the problem of western comics into three parts:
1. Unoriginality - It is mainly capeshit and even then it's always established characters or some alternative versions of them. And with those characters there is no real interesting thing besides the occasional high concept villain since they are always flying bricks.
I feel like this is a major problem created more by restrictions put onto writers due to concerns about canon built up over decades that limits what kind of stories they can do. It's a double edged sword since it stops writers from making a story where a character acts nothing like they normally do and also a stifler of interesting story or character arcs. It ends up creating stagnate worlds with very little to do in them since they're only allowed to repeat the same things over and over. That said, I also blame fans for this stagnation because often they are the first to bitch about the status quo being changed and then when authors relent and go back to the norm those sames fans will then complain about how stale recent works are.
Every blue moon you'll have a work come along that does truly breathe some good old originality into a series that then becomes foundational works for later series. You then get the problem of those foundational works being written by someone who truly "gets" the characters they are writing and is able to have a nice blend of keeping the old roots of a character while mixing in some new stuff (or entirely do something new and ignore all the whining from the gallery) being replaced in the next run by some who clearly
doesn't get the characters.
You'll also have bigger characters getting stuck in ruts of sort where writers don't really know what to do with them and they're too popular to mess with too much, think currently Wonder Woman is a good example of this.
With manga, isekai is the literal epitome of unoriginality since with most of them your eyes can glaze over during any info dump and you haven't missed anything since you've probably read that exact same set up thousands of times before. You again have those once in a blue moon isekai that are actually okay but still.
Compare and contrast Jojo that has more outlandish shit in every chapter than comics have in their entire run. This in turn makes the events in the comics just boring, I've seen more interesting and fun fight scenes in Chainsaw Man than every action scene I've read over dozens of comics (despite being in black and white and jumping around).
Personally I find Grant Morrison's work on a similar tier of what the fuck that runs through a lot of his works, it's a problem that a lot of comic authors play it a bit too safe. Do agree with Chainsaw Man point, I find a lot of comics sadly suffer from this weird stiffness during a lot of fights.
2. Creator worship - While it sucks that some manga will never end since the creators will play Idol simulator all day, it sure beats the current status quo in western comics where the same few people constantly write the same comics in the same styles and will destroy the career of promising new competitors if they don't suck the cock.
3. Lack of nepotism - Writing manga is brutal and series that don't stick gets outed pretty quickly, but it at least gives talented people the chance to reach to the top through their abilities (yeah plenty will get to the top by jumping on trends but still). In western comics? You need to be a part of a social clique to get your leg through the door and that creates the situation that the few comics that aren't capeshit are featuring "Scifi black latinx lesbians fighting white supermacy". Rather than interesting ideas like a city surrounded by hordes of naked giant cannibals.
Part of this I'd also say is publisher worry about giving new writers big series rather than slapping a big recognisable name that they can drum up press about. It's a bigger risk and a lot of western comics aren't known for being risk takers as hinted at in the previous point. That in turn creates big name writers with big heads that use their position to push out guys they don't like. Though some big names are actual poison like Bendis who's name being attached to something is a big red flag that it's probably garbage.
I'd also say the whole problem of people getting friends hired is just how the art industry functions due to it being fairly small. It's often the case that when a studio asks their staff about knowing anyone they could hire they'll typically vouch for their friends, this isn't a sin in my books and it's the norm. The bigger problem is studios not doing any quality testing on their end to see if said recommendation is actually up to snuff
or going back to the previous point, big names forcing said person in.
tl;dr Western comics are the definition of stagnation and lack of meritocracy.
Would more slap that onto the big two getting stagnate in their major titles because I think the indie scene has its own problems (like getting barely any attention or being slapped underneath the graphic novel separation). The really good western comics I put on the same tier as any of the best manga. It's like criticising all manga for Shounen Jump titles or Shounen in general when there are a plethora of other titles that just don't get the same level of attention. Shounen titles are the most translated because they have the highest readership, but most of them I can't stand, so I do find sometimes that manga releases here are having that same feeling of stagnation when it's all Shounen/isekai getting released.
I have no idea why I'm defending comics so much, feels weird.