Both variants need buffs:
Sorcerer because you need to pump alot into kassadin/one a-sol/tf or get lucky with multiple veigars to make it work, and there are like three counters to these sorts: double negatron, demons, double dragon, glacial, etc.
Knights because the 6 knight passive doesnt provide much of anything and stacked out assassins will still potentially one shot these people. Also knights DPS are largely mitigated by demon mana burn/CC in general
I don't feel like sorcs really need buffs, they work well for me. The only issue is that you can't do shit vs demons which are very common after all the buffs(atleast on PBE), cause no mana ->no spells ->no sorc
Knights also have massive issues with manaburn given they have the lowest AA dps of all classes, but on top of that their perk doesn't scale well and with 3!! tier 1 pieces, their lategame sucks even more, they are basically meatshields+Seju(unless she gets manaburned ofc)
To be honest, asides of still to much rng, manaburn is my biggest issue with TFT right now. For many comps it's basically like glacials but with higher proc chance and more damage, it just prevents your champs from defending them selfs.
I agree both - Sorcs6 I exclusively run with at least one Yuumi (usually aiming for two) because a full sorc 6 team is just not worth it. And Knight6 is fine against AS-Champions* but against anything with high DMG you basicly dont have a comp at all... 100% not worth it to build.
*honoring a single Seju tanking 3 Level2 itemized Rangers for 20 seconds leading to time out and elimination......
Sorcs don't need a buff they're a top tier team when geared correctly. Varus geared with Shojin or Seraphs, attack speed if possible. Morg or Lulu with locket(s) Asol with Shojin and Rabadons. Then just fill in the rest of the Sorcs and they're an extremely strong assassin proof team stacked into a corner.
sorc is fine, what you get hard countered by demons? will look sorc vs nobles and tell me how it feel having your 6 noble buff which demand 6 specific champions 
being useless just because you ignore it with sorc heavy magic damage, the only problem i can see that need fixing for sorc is veiger targeting and dragons being immune to magic [which i think is being changed in pbe?] .
knight i agree need a change for late game comp, 2 knights early is amazing but then it become non existence.
