It's been covered elsewhere on this forum, Rain 5G uses Strict NAT and there is no way to change this. Rain uses Carrier grade NAT similar to the mobile providers; basically the external IP assigned to you is also shared by many other Rain users as far as I understand. So in games like Destiny 2 and CoD MW the game will only place you with other players also on Strict NAT.
Around your 2nd point, to get a stable ping/latency, play with your antennae settings as noted by @name_less.
Manually set antenna to Fixed then cycle through the variations from 1-10 until you get the best speed. This will dramatically stabilise latency spikes.
"I had the same problem with random internet drops and massive spikes. What fixed it for me was going into antenna settings in "system -> antenna" and changed the 'Select Mode:' from 'Auto' to 'Fixed' and apply. You can change the 'Antenna Combine Index', it's the combination of antennas which can be used on the device. The arrows in red shows the antenna combination for the selected 'Antenna Combine Index', more details can be read in the user help manual (as shown below). The 'TX Antenna' is the antenna currently used, respective to the 'Antenna Combine Index'."
Thank you for the detailed info. I've tried with the fixed antenna settings, which made it slightly more usable, but not stable at all yet. I seem to have pretty solid reception and connection on the router, but no usable luck. I feel like I've tried everything, so guess I'll just have to wait.
Thanks again.