So I can only really speak to the MCU, not the DC stuff.
The first thing that's worth noting that the MCU is basically a soap opera but with superpowers (I would argue the same is true of the comics). And as with any soap opera, it only works if you like the majority of the characters, and so care about them. Much like the Spider-man and Batman animated series you watched as a kid, actually.
Secondly I think it's worth remembering that these aren't smart intellectual movies. They're dumb fun of the very best kind. Big bright colourful smile-inducing fun. Don't expect anything ground breaking.
So I think the "I feel like it's the same thing over and over again" can be a problem. Especially if you're watching the first movie in each characters series. Iron Man 1, Cap 1, Spiderman 1, Batman Begins, etc. These are all stories that are telling us how someone becomes the superhero that we know and love, establishing who they are. They all have the same basic pattern. Them getting powers (or having a need to build a suit or whatever), finding a bad guy/thing that needs defeating, and finding the strength within themselves to defeat the bad, whilst learning who they really are in the process.
To see what they can be once you get past that, maybe try Captain America: The Winter Soldier. I think that's a very different kind of movie in taking Cap and then putting seeing what he does in this tough place. Just The Dark Knight took the Batman established in Batman Begins and then starts seeing how this guy reacts rather than establishing a baseline. Looking at the animated series you mentioned I think it's interesting they don't even start with origin stories, they just jump into the soap opera of it all.
Finally, I think it's fine not to like them. It may not be that you're missing anything that would make them click for you, just that they aren't your kind of stuff. And that's fine. There is nothing wrong with missing out on things you don't enjoy.