As far as 5E D&D is concerned, at least in the level 1 - 15 range, optimization isn't really that big of a deal. Even if you're playing some sort of super-character, your success adventure-to-adventure will rely more on who you're playing with than what your party is doing. It's all well and good to be playing, say, a Diviner with Simulacrum and with a Planar Bound Earth Elemental, but if two of your party members of four are playing Beastmaster Rangers and another person is playing a Four Elements Monk (which has happened to me before in a Tier 3), you're going to have a rough time no matter what you do.