Frontier knows all this and as such need to release a Alpha which is as polished and stable as humanly possible.
An alpha is pretty much by definition NOT polished and stable, that is why it's called alpha in the first place.
If a developer is using several weeks of development to "polish" features in an alpha that could be a potential huge waste of resources. What if no one likes or wants these features?
I realize that in today's market, with alphas, betas, pre-releases and early access all over the place the line of what is a "finished" product is a very grey area, but I still think that FD should use this alpha the way it was intended. That is, a way to get early feedback on the game from us backers and then use that data to improve the product even further.
Let's face it, if they keep on holding back the alpha until it is "perfect" we will never ever get hold of it.
There is always going to be people criticizing the game, no matter when it's released or what state it might be in. This will of course also apply to SC when they release their dogfighting module in the beginning of next year. It's the internet after all, you can't get away from that. Also keep in mind that at this point ANY type of gameplay footage will be better than nothing at all. The only thing most people have seen so far (excluding the latest dev diary) is the prototype videos from last year and they aren't even close to what the game looks and plays like today.
Anyway, I suspect that they are further along in the development of this game than some people think and the alpha will probably be pretty stable and "polished" anyway.