Connectivity problems with SBG8300 upgrade

I've been a happy camper for years with SBG6900AC gateway and 100/5 connection but recently due to working from home I decided to upgrade to SBG8300 with an eye on maybe going to gigabit.

That did not work well. For several days now SBG8300 has disconnect problems, online conference calls quality is horrible, packet loss in Zoom is huge (not all the time but I have to ask "what did you say?" on Zoom every 5 minutes or so) and in general it's very unreliable. After reading the forums here I checked my power levels and here's what I have got:

Downstream:

(dBmV)

SNR (dB)

Upstream:

Power Level (dBmV)

I talked to Arris support and sure enough they say upstream level is too low and I need at least +45. I talked to Xfinity support and sure enough they say my signal levels are spectacular and there's nothing to be done. Though the rep mentioned that if I upgrade my speed it would be better. So I am basically being given the good old runaround. 

So my questions are:

1. Is this the end of the road, should I just return the SBG8300, scrap my upgrade plans and be happy with what I have? SBG6900AC didn't have these problems, as fas as I could see. Is there any other equipment option with modem/router which I could own and it would work with that I have from Xfinity? Is it just Arris being bad? I could try Netgear ones if they work better. 

2. Is it really true that signal power levels depend on the speed tier? I have never heard anything like that but maybe I was just misinformed before.