Not necessarily any harder than cutting steel pipe with a hacksaw, which with a good one can go quite quickly if you have a strong arm. The difficulty is that it's impossible for anyone nearby to not know what you're doing so you need to be EXTREMELY good at social engineering to convince everyone around you that you have a legitimate reason to be hacksawwing a locked up bike and taking it away.

A good public spot, preferrably with cameras nearby, is worth more than a Fahgettaboudit lock.