I looked at his buff/nerf history, and he never really received a nerf ever since Season 1. I have never seen him played competitively, even during moments when he appeared to be a good pick against certain champions.
However, in solo queue I have seen people say that Swain is OP, because of the ability to never die with your ult in the middle of a teamfight.
So... what's the problem with Swain?
problem with swain is he can ulti while zonya. same for fiddle, kharthus or heimer with his turret. massive dps while invulnerable is a bit moronic.
zonya is a moronic item btw. it should give 60ap, not 120ap. the active is too monstruosly op. an i dont understand why it also give 50armor. balancing op i guess
He's really hard to last-hit with unless you've practiced with him a lot. I wouldn't be surprised if that's why people don't like playing him (they don't get the farm they need, and so they don't do well.)
Swain is OP in SoloQ because he stomps any squishy who dares to get into his range into the ground. If you're up against a 
, you are basically guaranteed to snowball, and a snowballing Swain is just not fun at all for the enemy.
Also, he is way too underrated/-estimated, nobody knows how to play against him. Oh, and of course, he is a bird.
90% of champions that are played in SoloQueue but not in Comp - Have weakness that is exploitable with teamwork. In soloqueue the teamwork is non-existent so they flourish.
And yes, swain soloQ OP ;)
I just find him... boring. But that's my personal opinion. He has quite a hard time to CS.. But eh, aside from that, he's just not in the META. He's still a good pick.
His range is not great at all and was picked in competetive only in toplane vs melee to counter them, Most long range mages can zone him before and after 6 will outpoke him, but he can't return much dmg. Also people pick mages for their burst, not for their short range DPS and tanking abilities. If you are under siege, Swain can't waveclear like Xerath, Ziggs, Kog, Ori etc and will get bursted, if he tries. He is also immobile. Swain can snowball vs people who try to 1v1 him without ignite, melees without mobility to dodge his snare.
He has the most retarded under-the-tower aa animation in game.....
QED
EDIT: and of course....ignite sorta counters his ult healing...so...there's that
