You're quite within your rights to return your purchase. If as you say the only feature that you wanted was 4K/60 and we now know that that mark hasn't been reached then I can understand your reaction.
As for your other comments, yes, community is tiny and the choice of games is limited; all valid points considering how new Stadia is, but not something that wasn't known before IMHO.
The number of available titles has been known for quite some time now, so it should hardly be a surprise to you that the choice of available titles is going to be limited to begin with and for the foreseeable future based on the 2020 release schedule we are aware of (of course there could be other titles due out in 2020 that would tip the balance, but I'm not convinced yet to be honest).
Some folks are prepared to give it a bit more time to sort itself out, some not, there is no right and wrong side here, each to their own as to what they want to do. The advantage that you have is that you are still able to get a refund, so no money lost unless you've bought some titles already and have played them for more than 2 hours.
My own hope for Stadia is that my kids will be happy with it, no messing about waiting for titles to load, and personally I'm just happy to have another option available in the house that is quieter than the noise our XBox One makes when it decides it wants to kick the fans off at full blast.
So, good luck with getting your refund 
