Thoughts on the state of TfT from a diamond player
Right now, I think the most problematic aspect of TFT is the abundance of RNG elements. Now I understand that the game is inherently based around some randomness, but in its current state it feels like too much. Since there is a ranked TFT ladder it seems like Riot wants to have a competitive TFT scene, and toning down the RNG would help to showcase player skill.
I like being handed random champions and items to play with, that rewards creative players who can adapt to what they're given. I don't like having some players get 4 item components from minions and others get one or even none. I would like to see item drops normalized, so minions always drop for example two gold on the first round and one item each on second and third rounds. Same for the other PvE rounds.
Following the theme of excessive RNG, the current phantom and hextech bonuses feel either overpowered or useless depending on which unit they hit. Reducing a 3 star volibear carry to 100hp before the fight even starts is nuts, but you can also hit the warwick who's only there for brawler synergy. Same with hextech to a lesser extent. I would suggest making phantom bonus instead cause your phantom units on death to become untargetable and continue fighting for 5 seconds, and for hextech to give an additional 50%/100% base stats to all your items.
Healing and the grievous wounds mechanic are quite busted at the moment. Having a healing based unit like warmog's gnar or swain puts you in a position where your unit is either going to be an unstoppable juggernaut without grievous wounds or die far too easily with it. I would suggest nerfing healing items and abilities across the board and reducing grievous wounds to a 60% or 70% reduction rather than 100%. That way healing is less oppressive against teams without grievous wounds and not completely useless against teams with grievous wounds.
Nobles are another problem, they just feel bad to play. The three noble bonus falls off incredibly hard past krugs, but the 6 noble bonus is so strong it's worth playing three one star nobles just because you found a kayle. And that's the other problem with nobles, pulling off the comp is entirely dependent on finding a 5 cost unit. I think nobles could be fixed by changing the 3 noble bonus to give your whole team just the 35hp restored on hit so it's worth running 3 nobles mid-game, lowering the 6 noble bonus to 50 armor/mr, and adding Lux as a 3 cost noble sorcerer. This would make nobles much more consistent while tuning down their late game dominance just a bit.
Gunslingers are in a good spot right now with the addition of Jinx as a strong late game carry, but their itemization feels problematic. Cursed blade's effect is currently a balance nightmare. Dropping units down a level for the rest of the fight can have a huge impact for a single item. I think it would be better if it instead reduced damage output by 50% for four seconds and had its proc chance increased. This would give gunslingers a powerful defensive combination with hush rather than having a chance to basically delete a unit in one attack.
Demons are in a weird spot right now, their bonus is quite good but building a comp to take advantage of it is awkward. The viability of demons seems to scale in direct proportion to the number of darkin items you can build because right now the fewer actual demons you have in your demon comp the better. That said sorc comps with Morgana and Brand seem to do very well.
Rangers make me sad. Kindred is a disappointment of a 4 cost unit, doing little damage and having a powerful but inconsistent ability. Ashe is the best of the bunch, but I have more success using her in a glacial comp instead of four rangers. She's more of a support unit than pure damage, which is fine but leaves your ranger comp lacking in potency. Varus used to be solid damage, but his ability damage was reduced on top of his targeting being inconsistent at best. He would be far better if his ability targeted the farthest unit like Aurelion's does, even if it means further reducing his ability damage or increasing his max mana. Vayne is, well, vayne. Good rageblade/hurricane user, can't really solo carry, but at least you're the only one collecting her.
Other than the issues I listed the game feels pretty nice right now. Multiple team comps can do well, and most items feel pretty balanced. I think TFT could support a strong competitive scene with some polishing, which would be great.