I can't deny that a big blade makes some tasks easier, just like an ax makes some tasks easier too.
But overall, I think it depends on the survival situation.
Alone, on a forest covered island with no chance of escape or immediate rescue, sure a big blade is great (and an ax is probably better).
After all, you're going to be there for a long while and you need to build a more permanent shelter. You would really be homesteading until someone rescued you.
But if you are in the woods or desert anywhere in the lower 48 states, I think you would be better served with a good multi-tool and maybe a 3"-5" locking folder.
You're goal to survive is to either wait until help arrives (if you took the proper precautions of letting someone know your schedule and where you are hiking), or hike to civilization yourself.
The fact of the matter is that it is hard to walk in one direction, in the lower 48 states, for more than 15 miles without coming upon some form of civilization. And in some states, you can't walk 5 miles without hitting someone's house!
I also think that knowledge is much more important than what type of knife you have. I doubt if there has ever been someone who died in the wilderness just because their knife was too small.
When I go in to the woods I always have two things with me: a knife or multi-tool and a Bic lighter.
I have carried a machete or an ax or firearm or recurve bow on occasion, but I did'nt really need them. They were more for fun and experiance than anything else.
Good luck,
Allen.