Not according to Mythbusters. The chainsaw was clearly the winning weapon against zombie hordes. And hordes of zombies, too.
Alright: You say that the saw would be pulled out of your hands by the zombies. We're talking about a demi-god (Steve/Alex) that has indescribable strength, as seen both by the bow pull, carrying, and tree punching ability. "Rubbish against wet flesh"? If anything, that would be an ideal material to slice through, I would think (as far as I know, there is no actual testing of this for chain saws, but the whole behavior of normal saws on flesh is pretty clear).
Granted the chainsaw would be effective and efficient at killing zombies, however it would be a poor choice of weapon in zombie survival.
a) Splatter- zombie "virus" [whatever it is] is often spread through bodily fluids, you'll likely contaminate yourself and other nearby survivors. Even in a full biohazard suit you'll still run into visibility issues with zombie juice covering the visor. And the needing to wash off after (both yourself and the saw).
b) Range- with exception to speciality long bladed chainsaws, you'll be getting fairly close to the zombies putting yourself in a high risk of being grabbed/bitten. Especially when dealing with a horde.
Honestly- stick to firearms/crossbow (reload time)/longbow (strength/training) to kill them
before they get too close.
If you need a striking weapon, a spear would fare better for survival, easier to maintain/make, with the longer range and option to throw it if you have spare. Added bonuses of being lightweight and doubling as a walking/poking stick.
A second choice would be a hammer, probably a lump hammer/large claw hammer/hatchet on a sledge hammer handle. Sledgehammers, logging axes ect would be too heavy. You need to carry it around and swing it quickly.
However chainsaw would be a good option if you're going to die anyway (base is compromised and you're buying escape time for everyone else).
Though you may end up with something much much worse- zombies wielding chainsaws. For that I'd recommend running shoes and a slow, fat friend.