First off, I blood hate threads called "We need to talk" but I hate this thread already and I think you will too, so it's ok.
Second, this is not about plotholes or those minor hiccups in the story that you call plotholes. If you think any of this is about plotholes, turn back. If you want to make this about plotholes, I'll fight you. With rusty spoons.
NO.
PLOTHOLES.
So what is this thread about?
It's about that bizzarre habit Feige and co. have of making one movie about this thing, this message, this character development, and then immediately ignoring or undoing it in the next movie.
It's everywhere in the MCU.
It goes from simple stuff - Hulk in Infinity War vs Hulk in Endgame. Hulk's character arc in Infinity War is about Hulk not wanting to be Banner's emergency button. This leads to two different narrative threads: one is the expectation of finally seeing Hulk come back, and get some sort of closure in his fight with Thanos. The other is seeing Banner accepting the challenge and proving he can be on the team and fight alongside everyone else even without the Hulk.
Fast forward to EG: we see Banner following the gang still using the Hulkbuster on their first fight with Thanos, so it's clear that his conflict with Hulk is unresolved! Hooray, we'll see that storyline go somewhere, right? Nope, Banner merges with Hulk offscreen during the timelap and becomes this very neutered professor Hulk thing that never fights, never gets angry, and never confronts Thanos.
But wait, maybe it's a coronation of the other character arc, him not needing Hulk? Nope, he needs Hulk all day, every day. He's 100% Hulk now. Go figure.
Then there's the really bad stuff. Spiderman Homecoming ends with Peter turning down the Iron Spider suit to prove he doesn't need Stark, he doesn't need to be an Avenger, he's his own person.
Months and months of people complaining about Iron Man being in the movie, about Spiderman not being allowed to design his own suits, of Tony Stark taking a too big spotlight into Peter Parker's story. Awesome.
Literally the next thing we see Spiderman do is interact with Tony Stark and wearing the Iron Spider suit. Look guys, I know you want him in the Avengers, and you need him there, but then DON'T MAKE AN ENTIRE MOVIE ABOUT HIM REALIZING HE DOESN'T NEED TO BE AN AVENGER.
Shall we touch on Tony Stark basically retiring at the end of every movie he's in? Iron Man 3 ends with him blowing all his suits. The very next movie, he has 3 new ones. And again, the blame isn't on Age of Ultron. They knew he'd be in it. They knew the point of Iron Man is making new, amazing suits. So why make an entire movie about him not needing to be a hero and not needing to use suits? Why make him remove the arc reactor?
Natasha... poor Natasha. Where do we start? Oh, let's start from Banner. They're a thing, yes. She's going to appear in 3 movies after Ultron, he appears in 3 (or 4? I'd need to recount). You see both of them in 2 of them. They NEVER interact again. No closure, no acknowledgement. Nothing. It's the umpteen "let's have this thing in this movie that is a big shock, and then let's forget about it because we don't want to actually have a narrative here".
Steve makes out with his niece, and then she disappears from the story. What was that all about? Why?