I use my Xperia 10 III as my daily driver so I hope I can shed some light regarding your corcerns. What you can do for us is to let us know, what you mainly use the phone for. That way we might be able to provide better answers. Anyways, let’s cut to the chase:
I use these native apps daily / almost daily: Browser, Mail, Terminal, Clock, Calculator, Fernschreiber (native Telegram client), Whisperfish (native Signal client), Battery Buddy, ownKeepass (native Keepass client) and PureMaps (navigation app). So far the only real problem I have stumbled across is the browser crashing occasionally, but I can always restart the browser from the UI and get right back to where I was.
On the Android side I use work-related apps, banking apps and NewPipe. Everything else works great, but NewPipe crashes everytime I want to change to another video. However, this wasn’t the case a couple of months back, so I’m keeping my hopes up.
I charge my phone at night till 85% and usually I have around 25-35% left at the end of the day. Some days I’m using the phone really intensively, which means I need to charge my phone at the evening as well. The battery life could be better of course, but I have never been in trouble because of it and I don’t use a powerbank.
The UI feels really snappy and it is really fast to change between the apps once you get used to the UI. However, my last phone before 10 III was several years old iPhone SE, which may not set the bar as high as some other phones. The only instance where I notice lack of smoothness is when using the browser and scrolling up or down.