I have a Pinebook, with the same CPU as the PinePhone, it doesn't seem all that slow when running at the highest frequency, would be interested to know what frequency the PinePhone typically runs at.
Honestly, try browsing the web for a few minutes and it gets uncomfortably hot. Actually, I wouldn’t be surprised if some devices (mine included) have buggy hardware more so than the one you got, because I would expect much worse overall opinions otherwise.
And arm is not a new compilation target, so I don’t buy software differences being entirely the culprit, either. Worse battery life? Sure, that would explain it. But having trouble running a terminal and opening settings in 45 seconds is just criminal.
I really haven't had that experience in quite a while. I am mostly running DanctNIX or postmarketOS 22.06 with Phosh and browse with Firefox (with uBlock Origin - I also have a second Firefox profile that has NoScript installed for sites that just have too much janky JavaScript) or Epiphany.
It may help that the south of Germany is not super hot (just hot) and that I use Biktorgj's Modem firmware.
Edit, example: I am writing this in Firefox on postmarketOS while having 4 other tabs open and also two more apps (Tootle and Secrets), and the phone isn't even slightly warm.