Everytime I play Abathur I'm met with people that completely leave me on an island in the toplane, even when there's an enemy Tassadar relentlessly splitpushing or a guldan who can simply kill the wave with 2 spells. I really feel like abathur is NOT an offlaner, he's not good at pushing waves until level 7 and he doesn't push waves particularly fast. You need someone in your lane to provide you with safety and to make sure that the enemy doesn't just bulldozer over your towers.
I also think he's most powerful when he doesn't have to worry about depushing a lane, where he can help a bit in a skirmish botlane, then hat the wave top to soak the XP and head back to mid to save someone or secure a kill. His global presence is his power, but if you just leave him against a good splitpusher he has to focus all of his attention and resources in 1 spot while slowly losing.
Ofcourse his splitpushing and global presence is insane at level 16/20, but that's not what I'm talking about, his biggest weakness imo is being misunderstood and people not covering lanes with him early game. Take Sylvanas for example, Abathur has absolutely no chance of holding a lane vs Sylvanas, she can push very quickly and she can convert the minion that your hat is on, it's one of the hardest counters to him imo. He just needs someone to cover for him.
I currently play in high platinum and I play him quite a lot in QM as well and in both cases people don't really cover lanes as much as they should imo, it's a lot better in ranked though, it's rare for people to leave you all alone, but in QM it rarely ever happens that someone helps you out.