I have the same thoughts so far. Impossible to disable 5G network mode (no matter what the phone or apps show) and the extra speed isn't much compared to 4G+ while it has an extra battery cost (when it can't be disabled).I have a 5G on/off toggle in my quick settings menu. I assumed it would do as advertised. I'm not sure that it does anything except prevent the 5G indicator being displayed. It doesn't appear to change network connectivity or performance in any way for my phone.
Specifically, today I turned off 5G for testing coverage and speed using nPerf. With 5G "disabled" nPerf still identified 5G service exactly where I would expect to find it. On my return journey I ran speed tests every five seconds as I drove back home. The speed test identifies the connection type and reported 5G connections even though the phone displayed no better than 4G+. Actual speeds achieved were in line with the speeds obtained with 5G enabled (302Mbps max so far) , but not very different from 4G+ speeds (200+Mbps) before I had 5G working.
It all seems a bit smoke and mirrors to me.
I get about 90-160mbps with a good 4G+ signal, 110-320mbps on 5G. For browsing and 4K streaming, 4G+ is sufficient for me so far. 5G does give it an extra edge though, it definitely gives faster loading times and less buffering.
I won't do this yet on the phone I have coming today (I'll monitor my battery use first) but it was good to know we can.