I have turned suboptimal after a couple of years of playing 3.0 and been since then. The web is full of people who tell you how you should or should not play the game, they are also the same people who generally say that any edition is flawed to the point of being unplayable. In fact, they probably don't play at all. Not following them will only make your life easier.
If feats are not allowed to anyone, then you are sub-optimal versus who?

If you mean that you are allowed to take feats but choose not to, then see how many people around are claiming that it's totally insane to choose feats instead of ASI: they are about the same amount of people claiming it's totally insane to choose ASI intead of feats.
I think this is the only point when some optimization or rather some focus-fire may be important. It's only on narrow tasks however, not general tasks such as "melee fighting" or "healing", where it doesn't matter who is the best at the job because many people are doing it. On narrow tasks such as for example tracking, lockpicking or deception, it might be healthier for the group to have a dedicated character and have the others take care of other tasks (of course two dedicated characters improve the chances, but stepping on each other toes can be annoying and you'll have other tasks neglected). However, it's not so much a fault of the dedicated character not being optimized enough, but rather of the fact that two characters are investing resources into the same thing.