I think my space for "permissible character concepts" is much more broad than yours. This may be due to very different play goals. Clerics who refuse to heal and great-weapon melee fighters with a 12 Strength can still contribute meaningfully to party success in my games.
Again, my games are not so fragile that the lack of a dedicated healer will lead to a TPK. Potions of Healing are usually enough.
In a similar vein, my games are not so fragile that they have rigidly defined "roles." There are multiple ways to overcome my challenges.
I wonder if the sensitivity to un-optimized PC's is related to the particular demands that you put on your game and your group. It sounds like perhaps the challenges your group faces are significantly harsher than the challenges the game expects for most groups. I suppose that means you're all quite good at D&D, but for me, character diversity is a big gain that the expected challenges enable.
So when 5e allows for viable "pumpkins" as a default, that's awesome news for me. If someone wants to build an optimized character, that's great, but having diminishing returns for that optimization emphasizes that the game has a broad range of balance, and does not require you to fill roles, force people to play healers, or even guide people by the nose through what is a reasonable Strength for a two-handing front-line warrior.