It seems like Everscream is the only one that truly takes massive damage from this combo due to its size, which causes it to take damage twice from a single beam. Against the slightly smaller Santa-NK1 I was pulling numbers like:For a quick proof, try these swords against everscreams and santanks with and without projectiles
(beetle scale mail) ~1600 beam, ~4600 combined
(hallowed/monk/squire) ~1800 beam, ~3700 combined
Presumably, this is because Santa-NK1 is large enough that the beam can still hit it after the iframes from the blade have worn off. When testing against Target Dummies, it becomes rather obvious that small enemies are not meant to get hit by both the blade and beam in one swing.
So whether it's worth the risk or not depends on whether you think it's a good idea to stand on top of a big enemy like Santa-NK1 or Everscream while trying to attack with the blade. Personally I don't think it's worth it, and I don't think it's worth running a suboptimal armor set like Beetle, either.