David Villa: Goals 8 + 2 Assists (+10) playing 679 minutes (with like 15 shoots on target, getting completely ignored in some games, and barely getting assists or minutes to increase these stats)
Cesc: Goals 7 + 9 Assists (+16) playing 1414 minutes in liga+copa+champions (plus like 60 minutes from the Spanish Supercup)
The only reason why Cesc has "6" more (goals | assists) in productivity is because he has MORE than twiceminutes played than Villa. We could easily tell looking at those minutes that Villa would easily get those 6 goals if he had those 795 minutes Cesc had. You will notice that when he gets those minutes, he will get better stats than Cesc, I'm pretty sure.
So in therms of "productivity", Cesc isn't really doing any better than Villa.
Where I agree with you is that Iniesta should start every single time, and everyone knows that.
That's true, but I'm not speaking just statistically here. Cesc has been playing on great form and with quality. He is still pretty much the 2nd most creative player on the squad next to Messi right now. My point still stands that given the fact that he is the most prolific assist provider (by a decent margin) on the team right now (on top of being 2nd top scorer), he has high starting priority. If he was playing like shit, then Xavi and Iniesta and Villa would start no problem. But he's playing so well lately that we are much better off when he is playing.
Your stats are somewhat misleading too... for one, I'm speaking of only with Barcelona this season, not including Spain. Barcelona stats are all that's relevant when speaking about Barcelona. So Villa doesn't have 8 goals, he has 5, and Cesc has 6. But besides that... you can't assume that based off of the numbers Villa has put up in his few minutes, he would consistently be putting up those numbers given more minutes. Surely, given he keeps up good form, he could well be putting up good numbers, but you can't say well since his goal per min ratio is so-n-so now, given more minutes he'd score so-n-so goals. Too many factors. Though I do get your point that he has been very efficient and lethal, and I do agree.
My point still stands though. Although Villa has been lethal and very productive in the time given, Fabregas is still very crucial and overall the more productive/important player for us, thus why he's been starting over Villa. So is Iniesta. It's a hard case to argue that either of them need to make room for Villa, they are 2/3 of our best attacking force we have right now. Villa is the other 1/4 of our best attackers, but Cesc and Iniesta play a more varied role than he does, so they have the advantage there.
I agree with you wholeheartedly in that I wish Villa would get a lot more playing time. I'm just saying that it's a really tough situation for him to be in when taking into account how the whole squad is playing without him, like Bojan said. We kind of have an if it ain't broke don't fix it scenario.
Again, I really do think he'll see a lot more time as the season progression, so this is probably much ado about nothing in the big picture anyways. Villa has strong character, I think he'll stick it out. I'm not too worried about it, but we'll see.