I've not seen the concurrent app counter before, and still couldn't find it based on your double-swipe suggestion. Could be helpful. I'm not really trying to run that many at the same time. I am definitely a power user in the sense that I have Tasker, Resilio Sync, Nextcloud, and many other services that run in the background. That said, other devices don't seem to be hit as hard as the Fold, and yes the P6P got hit and slow almost as bad, but didn't seem to have as many issues with apps restarting.
I've played with that dev option and never noticed a difference in the past. I don't know what device default means, but I disabled it again just now to see the results.
It seems that when the Fold heats up, which is after fairly light use, it throttles like you say...and I think this may even impact the RAM or caching behavior somehow. When the phone is completely cool, I have a fairly pleasant experience. It's been so bad that I've contemplated building a new back for the phone case that's a heatsink.
I'm at 86GB system and 81GB apps, with 38GB files. 207 apps loaded. It's not like I'm trying to multitask or split screen or anything wild. No games, barely any media. It just feels like if the wind blows the wrong direction, this thing heats up and ruins my day. Especially if I even mention the phrase wireless charging to it.
Sure would love some non-Google hardware that can run this OS.