The biggest benefit of a laser solution is that it doesn't need to be in the same orbit. It needs to regularly intersect the target's orbit (or at least close enough to get in the laser's effective range) but that's a much cheaper maneuver.
In general, at the power levels in question the limiting factor is diffraction, not beam quality. There are a lot of variables going into it, but the numbers I've seen bandied about for orbital systems are on the order of 100km. See e.g. here: https://www.sciencedirect.com/science/article/pii/S100093611...
