Without going out of my way to look at the average content in most games like Smash, or just fighting/party games in general, I would have to agree completely. I dont know how you would quantify content from different games though, especially say, MMORPGs. That might be interesting to look into in the future though.
As for your point about additional stages, what you say is definitely true. More is still possible. Though, I do have somewhat an issue with the phrase "...all we are getting...". It seems to carry a connotation of discontent I dont fully understand. I am not remotely insinuating that was your intent, it is just that mentality has been prevalent along with that phrase and it does, genuinely annoy me.
Than again, I am not working on this game, I have no stake in it in anyway other then that of a consumer, so I cannot really justify feeling that way.