I don't want to discount what you saw, but I don't think Linux gamers are even asking for official support. If they don't want bug reports from Linux gamers because the reports would be "tainted" by an unsupported operating system, then they could have a banner on the submission page. I would argue, however, that they would be missing out on a lot of free bug testing where all of these companies are far too cheap to pay for proper bug testing these days.
At this point, Linux gamers would just appreciate the bare minimum being put forth with developers not breaking the games for them.
GTA Online has terrible monetization and Rockstar are openly hostile towards PC as a platform, but I wouldn't call GTA mediocre at all. There's nothing quite like the attention to detail or breadth of GTA games. If you've played a few GTA clones, you'll know what the competition looks like and it's not even close.