Marvel's budgeting from Ultron to Infinity War/Endgame - What happened?

This has bugged me for a while.

Ultron is known to be one of the most expensive movies ever made ($365-$440 million). And for all of it's flaws, I think the film succeeds on a technical level. You can see the budget of the movie on the screen - it looks fantastic and immersive. The effects on Vision and Ultron are some of the best. The big action sequences are phenomenal.

Fast forward to Infinity War and Endgame. They had budgets that were seemingly lower than Ultron ($325-$350 million). Now all of these budgets are taken from Wiki, so, yes, I know we should take them with a grain of salt. But we have to assume some things; inflation from 2015 to 2018/2019 is real. You have the big guys like Downey Jr, Evans and Hemsworth, who we have to assume got paid more for Infinity War/Endgame. Plus, IW/Endgame and much, much bigger casts than Ultron. Hell, Endgame basically had all of the MCU in it. So, we have to assume a larger percentage of the budgets of Avengers 3 & 4 went to paying the cast. So... they spent less on production/effects?

I think from a technical standpoint - Ultron is probably the best of the MCU. And Infinity War/Endgame are step downs. As epic as the final battle in Endgame is - seeing all the people - the battle itself is just... not great CGI. It's bland and flat.

So... were Marvel/Feige just cheaping out on the budgets for IW/Endgame when it came to production/effects? I understand the importance of getting the whole cast, but also... this is the finale of a huge saga. Didn't they want it to look good? Or at least as good as Ultron looked?! Especially in retrospect now, with seeing how films like Quantumania, Love & Thunder, The Marvels and now Brave New World, how these films LOOK. Now, I can get behind a cliched super hero movie script; the good guys got to save the bad guys, and I'm down for that. But at the very least, these movies used to be technical spectacles. I saw Ultron on the big screen and was totally immersed into the world, regardless of the janky plot. But now... do they even care about the effects? Where is the money going?