I feel that the only relevant factor in hiring should be competence. How do you define being well rounded, and how do you measure that when you're interviewing? Is that just a code word for being someone like you?
So a competent employee who is a bore, is rude to coworkers, makes sexist/racist comments is fine. Okay.
...unless you define 'competent' correctly.
you can be a competent solo developer and still leave a team strictly worse off with you than without. i've seen it happen - people who subtract so much by the sum of their bad interactions with people that it outweighs any value their work adds.