This thread is making me miss 80s and 90s anime when studios were still running on bubble era budgets, could pour insane amounts of money into well-animated films, and still make a profit most of the time. There's still the occasional well-animated show today, but not nearly to the extent of those two decades.
But there's the problem, you're comparing classic MOVIES to modern SHOWS, that's not quite fair, it's like complaining that Adventure Time doesn't look as good as The Lion King. Gaf had this problem like a year or two ago where everybody was just acting like classic stuff always looked better and to "prove" it they started posting screenshots that "conveniently" used movies/OVAs from the classic era but then used shows from the modern era and of course focused on quality shots for the former and bad shots for the latter. Thankfully somebody fired back with examples from actual shows from the classic era and some of their bad shots versus the new era and their shows' best shots to show the other extreme. Plus, that's the problem with looking back at the classic era, not many fans are capable of remembering the stuff that actually sucked and remember just what worked because that's generally how memory seems to work for entertainment. Just check out Bennett the Sage who does a series called Anime Abandon and he's found a TON of classic era movies and especially OVAs that are total garbage.
I mean, animation studios like Kyoto Animation, Bones, Madhouse, Ufotable, Trigger, Studio Wit, etc. have made some amazing looking series. I think the only period of anime that had it really rough when it came to animation was roughly 2000-2002, that was when they were transitioning their style of animation and as a result a lot of shows looked rough.