Don't know about winning against Shamrock, but at the time, WWE had plenty of guys who could've brawled with Shamrock and given him a run for his money.
Big Show (size and athleticism), Undertaker (size, athleticism, agility), Kane (size and strength), Kurt Angle (wrestling), Faarooq (size, tough, football player, huge), Triple H (size, tough, will to fight), even a guy like Stone Cold, a 6'3 260 pound redneck full of muscles willing to fight is no easy fight for ANYONE. And there were others like Bradshaw who wouldn't be a walk in the park either.
MMA fighters aren't gods, even the best ones. Maybe the ones today, but Shamrock fought many pro wrestlers in MMA and lost numerous times. A fight is a fight, and muscle combined with anger is a crazy weapon set.