Flask makes early game too easy for lategame champions
Some champions have very weak early in exchange for beast lategame, these champions are supposed to be risky champions during early game and get rewarded for getting trough it with massive lategame potential, I am thinking here about Nasus, Veigar, Kassasin, Jax (kinda). The thing is, right now, flask makes it a bit too safe for them early game, most of the time they can just farm taking a lot of damage and healing with flask + 3 potions until level 6 or more where they can't be stopped no more. Now I am not saying they CAN'T be shutdown, but flask makes it a bit too smooth for them, especially for Nasus and Kass with their respective lifesteal/shield. Flask gives 120 health per charge (renewable) and potions 150, that means someone can heal for 810 health before really taking damage (that's without other form of healing) and spam their skills because of mana regen. Now I know that if you get flask you aren't getting a Doran or something else, but the difference on the long term for lategame champions is so insignificant, it pretty much doesn't matter.