Myriad balance issues as a result of Hi-Rez adding new weapons and items with no rhyme or reason beyond needing more sources of revenue, in the process worsening some of the core issues the game already had to begin with.
One of the dumbest things they did in the last patch was add powerful shields to base assets which many weapons can't take out, making generator play even more attractive to a lot of players and generally keeping players from attacking the flag stand since turrets are so accurate and powerful. Pubs boil down even more now to massive defensive stacks, which is just dull. It was an existing problem that Hi-Rez only exacerbated.
Pickup games can be enjoyable if you manage to get with players who aren't obnoxious, but that is far from a guarantee (at least in the US), and the only reason pugs work at all is due to players ignoring base assets after the first salvo, outright banning various imbalanced weapons/items, and keeping teams limited to 7v7.
Handing over modding/mapping tools to the community is the only thing that can potentially save the game, though it may be too late regardless. The player count has been extremely low for a long time, and with Hi-Rez unceremoniously bowing out, it'll only keep dwindling.