Actually, yes.
Warning: spoilers:
The game starts with the real guy, Desmond something, gets rescued by the girl who was an undercover assassin or something. There is a little bit of fighting here, but mostly running and trying to sneak past guards. this bit shows that Desmond is a real pussy and can only throw a decent punch once every year or so. Figured he would have learned something from his time in Altaïr's shoes, but aparently not.
Then, after playing as Ezio for a while, the game returns to real world and suddenly Desmond can parkour just as well as Ezio could.
Well, this isn't quite right, he felt a bit more sluggish and unresponsive, so perhaps not quite as good, but still pretty impressive for someone who hasn't actually trained in...well anything.
Then, at the end of the game, Desmond has finished going through Ezio's memories and is suddenly a badass assassin. He even gets the hidden blade Ezio used. Only one though, not the dual hidden blade, which for the record, was extremely fun to use. Stabbing two guards at the same time, awesome. Stabbing a guy though his eyes, sweet.
Ehrm, back to what I was saying.
Their hideout is attacked by the bad guys, and Desmond fights them off, fighting just as well as Altaïr and Ezio.
So yes, there is "real world" fighting and the plot holes left by his sudden transformation into awesome assassin are the size of galaxies.
That said, I like Desmond's personality better than Ezio's. But Altaïr was best anyway, probably because he was a real assassin, and not just a pussy with skills.