Well definitely plausible--FS fighters do that already.
However, it works both ways. SW can take out beam cannons, FS can take out turbolasers. Those SW fighters would have to work fast to keep their fleet from getting beam'd hard, and the FS fighters would have to work really hard to reduce an SD's armament in time to have a significant impact on combat.
Though I do have to say that SW fighters often look like they're surprisingly thinly armored, whereas FS ships tend to be heavily armored. If they have to resort to ramming, my vote's on the FS ships.
Here's one thing I've wondered about the Lucy--where the hell is it's shield array? It's always seemed like it's integrated into the hull of the ship, or is inside the ship, unlike SW shields. That might hamper the hail-Mary photon torpedo a bit.
Mal totally pwns Han.
In terms of each universe's bad guys, I think Shivans are more bad-ass than Storm Troopers. Let's see Vader and his minions try to pull what they did on Leia's transport on a Lilith or Rakhshasa. I have a feeling it won't end well for them. Vader might survive, but given an ST's accuracy rate... I think the ST's are crispy bacon if they try to board a Shivan vessel.