I don't know if it's simply poor RAM management on iOS 13 or if there's really just not enough RAM for everything the firmware now does but I've encountered more possibly memory related issues on 13 compared to 12.Pretty much how I feel as well. I've never actually found 3GB to be limiting on my iOS devices so it wouldn't be a deal breaker, but of course I would prefer more RAM.
Frankly, the fact that it has an A14 was already more than I expected in terms of specs, and since I don't multitask very much on my iPad anyway, the better processor will probably do more for my experience than more RAM anyway.
I've been getting more "This page has crashed and has to reload" errors in Safari (possibly due to being heavier desktop version?). They occur as frequently on Air 3 and Pro 10.5 (usually after sleep or app switch). They're noticeably more frequent on 2GB RAM iPads. Sometimes, the tab would even go into a crash loop but the problematic web page always loads after a hard reset.
There are also times when I lose the Full Page PDF screenshot in Safari or the Files app stops working (has sidebar but opening iCloud Drive or On My iPad just shows a blank). As before, hard reset fixes things. It just sucks especially in the case of the Full Page screenshot because that could mean losing the page I'm trying to screenshot.