Yeah, I understand this sentiment. I think I'll have to hark back on what was said somewhere earlier: Valve Devs are really quite headstrong in going with whatever the best idea is, not with whatever the community asks for. They don't often confuse the two.
I'll try to exemplify the kind of interaction I think we'd miss out on, if we didn't have public forums for existing hero design: I recently posted about Silver's Lycan form. I suggested, among other things, some new movement mechanics, all intended to make her Lycan form feel more "werewolfy" and "weighty". My post didn't get much attention, but when I posted the same thing on Reddit it did get quite a lot of comments. There were a number of good suggestions iterating on my ideas and adding new ones.
Basically, someone suggesting a design change has ostensibly identified an area for improvement in the original design. Once that area is identified, I think it's valuable to have a lot of people put their heads together and think about it. The fact that there's a community of people who are interested in game design and willing to do this for free is awesome, and it would almost be silly not to take advantage of it.
Again, I want to be really clear that what I'm talking about is quite removed from discussing hero balance. I'm sort of presupposing a philosophy where you try to make an awesome design first, and then balance it later by adjusting the numbers. In that sense, my idealised community members would be talking just about game design, in the way that people do on this forum when they talk about new character concepts. The closest they would get to talking about game balance would be stuff like "hmm... this seems like it would be hard to balance", or "obviously, we would have to strengthen/weaken other parts of the kit to accommodate this change".