Basically, as stated a million times before by many others before me, take out the sections that people complained to have and now aren't utilizing.
However, my main concern is the Games Universe, it seems a bit all over the place with the sub-forums only drawing a few people at a time. Nobody's posting in some sub-sections, it's as simple as that. If it's not active and they complain more once it's taken down, they can go to Upcoming Games or Popular/Classic Games.
There are four sub-sections involving Call of Duty. There are currently 130+ people in Call of Duty Series, while the others aren't quite as active (aside from MW & IW). Just throw those in Call of Duty Series and people will still go to it and use it. I don't believe there needs to be multiple sub-sections for one series despite the current spotlight. (Same goes for Battlefield 1/Battlefield Series.)
TLDR: Delete inactive forums and merge those that are popular so there aren't 500 sections.
I know my ideas aren't perfect and there are short-term and long-term pros/cons to changes such as these on a forum, but with enough thought and a little bit of effort, I don't think this would be a hard thing to solve.