I use to play on that and it was fine. Even if not, you’d get a notice about being switched to offline mode. This isn’t your problem.
I’m guessing you were looking at the task manager or something similar showing total processor utilization. With gaming, it’s common to only hammer one core, while the others are lightly loaded, which can show up as a light total cpu load even if that is the bottleneck
You definitely should be doing better, though. Try turning developer mode on in the settings. It’ll show a new toolbar at the top and one of the settings (I think in the windows tab, but not at the computer to double check) will have an option to display the fps. When that screen pops up, it’ll show the frame times of the CPU and GPU, and indicate which one you are limited by. Telling us that info, or screenshoting and posting it will tell us where to start looking.
If you have anything in your community folder, that should be moved out temporarily just to rule out any third party conflicts.