On the need for an 18 being a myth, thats largely dependent on the system. 5E is fairly forgiving of a spread out stat array, but PF2 would be down right punishing. The system math is so tight in PF2, if you fail to maximize, your PC will be completely ineffective. That was a design choice. Interesting enough, PF2 doesnt use rolling for stats, but a system that determines make up based on ancestry, background, and class. However, the choices seem to matter at face value, but all usually come out the same int he end. There really is only 2-3 functional arrays in PF2.
I think 3E/PF1 had the concept correct, it was the math that was a total mess.