I want to make it clear that I actually hate the Burly ability as listed. Even from a cinematic standpoint it's a little nonsensical even if only limiting to what you wield alone. Yep, that guy can now wield a heavy blaster rifle like it's nothing but a knife...the knife however is still the same though...yeah he's weird like that. The whole thing needs a quick rewrite. It's just that I am a rule lawyer at heart and, in my humble opinion, RAW is extremely clear cut here.
Well, a Heavy Blaster Rifle is actually 9 encumbrance, so that would still take up a good amount of a character's encumbrance
but sure, the talent could reduce a regular ol' blaster rifle down to 1 encumbrance, which is the same as knife.
I don't think it needs a rewrite in that regard. It just makes it so that the character is so strong and bulky that a rifle can be handled with the same ease as a knife. The knife still takes up some physical space...it doesn't become a "0 encumbrance" item, because that would reduce its effective encumbrance to 1/10th or 1/20th of its original encumbrance (because rules).
Since encumbrance is an abstract number based on weight, mass, volume, and shape, a minimum of 1 sounds like a good place to stop for me. The knife is still the same in that it's the lowest possible encumbrance rating for a small weapon.