You've hit it spot on. I got a light phone years ago to help cure my cell phone addiction, but it was too problematic. I still need to use the "tools" of my phone - things like Maps, Uber, authenticator apps, texting, etc., but I just wanted to block the "dopamine dealers" like social media and the browser.
The best I've gotten to so far is to permanently enable "focus mode" on my phone. Of course I can still disable it, but I've noticed the number of times I just automatically start browsing the web or whatever when I'm even just a tad bored, and having those apps blocked is at least just a reminder to me of "Do you really want to do this right now?"
At the moment I use greyscale mode on my Pixel and have uninstalled apps, only using them in the browser if I "need to." It's not much, but adding that small friction helps somewhat.
5G is more than future proofing, at least where I am, 5G is deployed at new lower frequencies (taken from broadcast TV) that provide for more full coverage. With my new 5g phone, I have less dead zones than my old 4g phone.
We have seen this in action as many Cellspot and other signal booster users have retired these devices as the indoor and basement cell coverage improvements of 5G deliver better service than the DSL or satellite back hauled micro cells these users used to have at home.
If 4g only makes your phone get stuck searching for signal and 5g would find a signal, turning on 5g will help