sure they are. would you consider a lottery to be a sound investment just because you won it once? look beyond the stats and consider the plays that produced those stats. if those plays are flukes, then so to are the stats.
and in other news, i haven't died yet, therefore i'm immortal.
You can and you can't do the "well without this big run/catch" thing. It truly varies from player to player:For instance: You really can't do it with Desean Jackson. He is the essence of the big play - he doesn't get that many total receptions each year, but he has a high ypr because he is so big play dependent - and he's that explosive on a weekly basis. His value comes from the big plays - the "take away that big play" argument is stupid with this type of receiver. Just add the risk of no big plays into his value, and then take him for what he is: a big play artist.
(note - he can evolve as a receiver and become a guy with more catches, less big plays, and more consistency. The type of player is what matters, not the specific name)
It's probably ok to do it with Roddy White. His value comes from his consistency, not from his weekly 40+ yard TD bombs. He's a target hog, he gets a ton of catches, and he derives his value from his consistency.
So with a player like Welker, it's safe to say "Well, he's probably not gonna have a lot more 99 yard TD receptions. That seemed like a fluke."
But with, say, Chris Johnson, you can't just take away the big play. The 55 yard run is where he gets his value - you have to be aware of the risk that he doesn't have that run, but he has produced it at a higher rate than many others over the course of his career.
In short - both of the groups at play here are wrong. You can take away the big play to get a better idea of a player's performance. That being said, you also can't ALWAYS do it. Individual player types do matter here.