If they are one of many groups, fine. If they are one group, HELL NO!!!
They way they play is light years form how I play. Actually, I am not sure if Char-op is how they actually play, but that mindset is not mine, nor my group's.
Actually, it's probably better for your group that they do so. Otherwise if you end up playing with someone who optimizes - and roleplays - their character, you will get to watch as your sword-and-board fighters see the batman wizard. And they won't be annoyed with you forcing them to self-nerf to disguise the fact that his character could probably tear apart that from-the-book, 2 CR lower monster you all nearly died to last week.