How big of an issue is it to leak this information? Disregarding the fact that many sites easily leak this info, how much security is actually gained by obfusca

How big of an issue is it to leak this information? Disregarding the fact that many sites easily leak this info, how much security is actually gained by obfuscating what usernames are taken? It seems to me like two factor authentication, rate limiting logins, good password rules, and properly securing passwords provide much better security then obfuscating usernames. There's always a balance between security and usability. I don't think hiding username availability provides enough security to justify the harm in the user experience.