i feel like swain is too binary and its way too easy to play around his kit. his kit has "too" much counterplay.
in laning phase, his basic cooldowns are way too high and do very little damage. with a 14/18/10 second cooldown pretty much all champions outtrade him early and the thing is that enemies just have to walk out of your q and w.
w is straight up impossible to land now with his q nerfs. before, q was instant which means when you used w, you could immediately q instantly to increase the chance of w landing. the projectile time on his q makes it way too easy for enemies to avoid most of the damage. his e got nerfed and e + ult doesn't do enough damage to chunk anybody low unlike anivias e + ult.
almost any champion in the game can straight up 1 v 1 swain by not walking into his q when trying to fight him, hes really only good in team fights but at that time you can just kite him and wait for his ult to run out, or just buy grevious wounds.
the only thing good about him is that hes one of the few champions that can utilize zhonyas, and he snowballs hard, but hes useless when falling behind.