Here's my $0.02.
I've run for hundreds of players. They fall into two groups.
1. I'm here to win. This is your typical optimizer. He/She/It wants to play X to the best that X can be played.
2. I'm here to Roleplay. The fun comes from being a cool character. Lets face facts, aging isn't that useful in combat if all you have is, "I'm gonna live for centuries!" Games don't last for centuries. Yet, I know of a few players who exclusively play elves for THAT REASON ALONE.
The first player enjoys the idea of beating what ever challenge the DM has. The second would be happy creating a new breed of horse and RPing being a horse breeder.
So, I guess it's like The Sims vs World of Warcraft. Both involve an Icon running around the screen. One has more swords.
But in the end, as they play, and the longer they play, the more they OP, just not in ways the other one understands. Finding a way to create the ultimate Magic Missile caster, when Shield cancels the spell in one shot isn't very useful for "winning", but can be fun to Role play as "master of Missiles."
Everyone OPs, it's just what are they OPing towards. I've never seen a player cripple his PC and make him worse in every regard. There was ALWAYS a reason. It just might not make sense. They might suck at the rules.
Tell me this, when was the last time you handed out a metal to a PC? You know, purple heart? Silver Star? Metal of Honor? What do you give the PCs if the NPCs are grateful? Gold and magic. Had an adventure where a kid's kitten wandered into a portal in Waterdeep and was lost in Undermountain. The kid wanted to hire adventures for all her money 1 silver, 4 copper. In the end, after expending WAY more resources then they got from the monsters, they rescued the kitten and turned down the reward. They got cookies the next day.
Now, I just have to say, "hey, remember the kitten adventure?" And they do. When I say, "Hey, remember the orc adventure?" They go, "Which one?"
Some players want a bigger boom stick. Some players want cookies. That's all there is to it.