I mean.. that's not a feature. That's a bug (likely due to RAM being full). I rarely if ever have this issue, but I do remember it happening at some point, but that's definitely not a feature that iOS thinks is better.

Really? I mean, I've seen it over ten years of usage, and it's never been any other way, so that sounds like a deliberate decision. At the very least, not using internal storage -- when RAM is needed for something else -- is a decision.

Mobile device OS's do not swap to storage because the typical mobile storage is bottom-of-the-barrel eMMC and the wear-and-tear of swapping on the flash would be a killer.

It would only need to do it in the few occasions when the tabs have filled up the available RAM and they're large enough to be worth dumping. iPhones use bottom of the barrel storage?

I see that sporadically but it's uncommon enough to be noteworthy on an iPhone 11. Do you have an extension installed or are switching to a very RAM-hungry application? I typically only see that if I switched over to do something like edit a video.

No, nothing RAM hungry. Only extensions are adblockers. And it's an iPhone 8, which, yes, I know, is from the Dark Ages where no one could ever expect any amount of data to be stored ever, but this has happened with every iPhone I've had back to 2012, including ones that were bought close to release.