Nevermind. It's actually quite easy to get all/most of the online achievements legit. 2,000 gem can be a grind though. I've played 3 or 4 hours online and have 1,5xx. So you just have to find the right time when other people are on.
I will add something that might help others that I found out. Once you play a match with a few people, create your own after and set it to 2 max players on king of mountain. Then collect gems for about 2.5 minutes, go to recent players and spam invites. Usually someone'll join and match will end soon after, saving what gems you got. It's hit or miss sometimes, but when it works, your guaranteed 90+ gems depending on how many to get after the person joins.
I'm just so glad I snatched up all 3 DLC's when I bought the game.
Anywho, good luck to anyone who comes here looking for online achievements.