Yeah, I'd prefer a Salgant who is an entirely decent person, and not at all complicit in Maeglin's treachery. I also find it hard to believe that the House of the Mole would help him assault Idril, kidnap Earendil, and accept his orders to stand aside and allow the Orcs to sack the city. There's just no way. Maeglin was compromised, but I can't imagine that other Noldor would have helped him once they realized he was a traitor. Some would be in denial until they heard it from Idril or Tuor's own mouth, out of discomfort at what that makes them. But I'd much rather see the whole House of the Mole unanimously defect from their lord as soon as they learn the truth, with several deliberately staying behind to fight to their death against the invaders because they feel dishonored by having served Maeglin.
Re obesity: OK, I belive you that obesity can result from overeating healthy food, but yeah, purposely overeating isn't an Elvish trait either. Elves are distinguished as being vastly less affected by bodily desires than Mortals are.
Beleg, I think, is described as of great girth because he had a huge pack hidden under his cloak in that passage . That is, I think the girth was the pack, not Beleg himself. I could be wrong.