Old Swain was undeniably better. New one's running 47% winrate this week. Not the best.
New one though I really feel like might only need a small buff to be good. That is to reduce the delay time on his W animation by 1/4-1/2 a second and remove the minion damage penalty.
As I learn his kit better, his E, Q, and R don't feel incredibly out of whack. He's techy, and this new version of Swain is much more like Graves, burst damage instead of the long sustain lane - you have to burst hard when you burst, and then accept that you won't burst hard again for a minute and a half when ult is up. But the damage is real and he can get kills if he bursts hard.
W does not feel good. And I despair about his new waveclear. It doesn't feel good to take more than five seconds to clear out a large wave at level 15 with 500 ap, and a lot of that is because his W was deliberately made kitten-weak against waves. It's okay for vision, but you check one bush and then it's on cooldown for ten seconds? As a laning/damage ability it is almost useless - bad for waveclear, trivial to dodge by champions due to the long animation delay, even more so at higher levels - which I feel will really reduce the chance that he sees professional play.
Therefore I feel like he'd be oodles of fun if W got an animation speed buff and the minion damage penalty removed. Riot clearly didn't want it used for that purpose, but I really feel like these changes may need to happen to give him a kit that feels full and real and brings him back to 50%.