Not sure it's so much size of the community, but more it's make up combined with in general how easy the game(genre really) is. At this point most people just want to throw on their Hand of Doom/Kurse Gem and go full out dps since there's not much incentive to do otherwise. Cosmics to a degree can benefit from actually having a balanced build, and I always build some defense/health on all my characters as it does make a difference.
You're also right that most have no clue how stats actually work, or at least how to maximize their build via damage rating/crit/etc. There are a few regular posters that I've found to be good theorycrafters, though most seem to be barely playing anymore, at least until some new content arrives. Also didn't help when the person who actually came up with the most accurate dps formulas ended up getting a job with Gaz, though they did repost his threads on the Guides section.
Anyways at this point with the way they standardized most all powers via the tags system, it's usually pretty easy to figure out a decent build once you seen those same abilities across multiple heroes.