On the topic of Swain, he's actually one of the harder champions to play, since he needs SO MANY STATS. He wants AP, he wants mana, he wants HP, he wants mana regen, he wants CDR, he wants armor, he wants MR, he wants magic pen...
Not to mention you have to decide what order to use your skills. Torment first is the most damage, but least reliable. Snare first guarantees your whole combo, but is hard to land. Slow first is shorter range and is lower damage, and has some of the same issues as snare against mobile targets.
Combined this with his frankly ATROCIOUS farming skills, which are probobly the worst in the entire game [Especially after they changed Morgana's puddle to help her score lasthits with it later in the game instead of being doomed to be stuck at whatever CS she came out of lane with], and you have to play Swain really well to do well.
Luckily, his Level 3 and 4 is probobly the strongest in the entire game as well, and he can snowball off that.
I'd actually call Swain as 'Feast or Famine' as LeBlanc, if not more. Except he can come back somewhat with assists in teamfights by simply pressing R and dying. He's mostly a non-issue if not fed, but at least does SOMETHING.
But likewise a fed Swain is an unstoppable rampageing beast, or takes so much focus you win anyway.
I'd like to see some minor changes to Swain to make him actually be able to farm without having to blow his long C/D snare [And level it up first!]. IDK, make his Ultimate deal extra damage to low HP creeps [But have that extra damage be ignored for HP restore purposes] or something.