Swain was overnerfed
So swain finally got his turn on the nerfing block. As a swain main, I didn't actually realize he was nerfed for like a week after it happened. I just thought I was on a terrible losing spree and then it dawned on me. Reducing his snare from 2 seconds at all levels to 1/1.25/1.5/1.75/2.0 was a significant drop. Swains early game offensive capabilities were pretty strong. Even at early levels, if harassing effectively...that two second snare was usually enough to guarantee a kill. I can totally see how the design team wanted to take some of the punch out of Swains laning phase, and this nerf did pretty much exactly what it was intended to offensively.
The problem here is that swain has zero mobility, and this pretty much gutted him defensively. Swain is extremely reliant on landing snares to survive ganks and dives. If you get ganked you have basically have two choices. Miss your snare and die, or land your snare on your laning opponent and their jungler simultaneously and still die because it's only a second and you took like a third of a second just on the cast animation alone. Obviously, this change was designed to force a choice as to which skills to take. Previously, it was one point in snare and then maxing laserbird and E. E is absolutely mandatory because it makes up so much of Swains damage. But even with the RIP laserbird philosophy, and maxing W first...it still doesn't get to be significant enough to be of any use during laning phase. Level 4 only gets you a 1.25 second snare on a massive cooldown. If you're willing to trade the extra damage from E, then you're only looking at a 1.5 second snare at level 6. But thats going to come at a significant cost in trading potential. I personally cant bring myself to take a third point in snare until 7 which leaves me at 1.25 until then.
In summary, basically Swain's offensive nerfs were much needed as he was oppressive in lane. But defensively he needs something to balance it out. Just a little bit of movement speed so he can survive...anything. Or even better, have snare give him a temporary percentage movement speed for each enemy hit and he'll be right where he needs to be.
Edit: Alternate suggest by Alfavhunter
Make it double in duration when swain is under 40/55/70/85/100% hp. The duration is doubled to 2 seconds when the condition is met
So if swain wants a stronger snare early on he either has to level it first or sit in a danger zone of under 40% hp
This also makes him stronger when losing lane and a danger for tower diving
His snare is still weaker early unless he is in a danger zone of hp, which is usually when he would get dove, it's unlikely for someone to dive a full hp anyone when not severely ahead as is