Hey Jaari, yes, I've used the /cofh TPS commands already to do a lot of monitoring. Have also used Opis and Clear Lagg's TPS checking to cross reference. The bot my friend made for the Discord server that interfaces with the server also has it's own TPS checker. Results all differ, but usually not by much.
As of my current checking, it's 20 TPS with one player on, but still reading at 36.259ms, which it shouldn't be at. (6.312 TPS at 158.40ms with only 4 players on)
If it wasn't clear enough, it's hosted by a friend of Poptart's on his own box. It's a 12 core processor, which is honestly useless for just about everything the box would naturally be used for, but oh well, I can't change that fact. I'm assuming I'd be correct that it's for sure the processor though, and most likely the excessively low GHz, based on what you're saying?
If that is indeed the case, do you suppose OCing the processor to try and get some higher values would be a good idea/safe enough to attempt?