Being weaker than a minmaxed combination that you want to always have also affects decision and behaviour. Role playing doesn't stop when initative is rolled. A half-orc wizard for example will likely use more touch spells than a gnome wizard. While an elf wizard is better with rays.
And that explanation above is simply bad and an attempt to retrospectively explain why a half-orc could be weaker than a halfling by default.
Expanding on this, let me give you an example:
I play a Tiefling Wizard. I have 16 in Int, 14 Con, 12 Dex, 12 Wis, 10 Str, 11 Cha. Say that was a dwarf instead. Hill Dwarf. The stats would now be 15 Int, 16 Con, 12 Dex, 13 Wis, 10 Str, 9 Cha. I'd drop con to 14 to get Charisma to 10, put another point into Wis to get it up to 14, one point left. With a +2 modifier, Int is still the highest I can use effectively, I would still use it. It just has a higher chance of missing/not working. I could, also, get Dex to 14 if I put Wis down, but that would change the Mind focus of the character, and would leave me with a shitty dagger as the only weapon, and even then, it would be on par with my spells stat wise. In the end, I would play my character the same, just less effective.
