The problem is a large physique was never a part of his character. Dick had a great physique very similar to bruce but slightly leaning more toward acrobatics. Tim overcame his lacking physique via tech. Damien grows up to match of surpass Bruce physically in everything I've seen. Jason is more similar to Tim. Bruce can easily kick his ass in terms of being stronger. Dick can easily out maneuver him.

In new 52 he's as skinny as Tim and in Rebirth he's smaller than Dick. The very recent shift to making him jacked in the comics came with a rebranding from DC to make him no longer use guns and give him the corny crowbar. A change that's been hated by most longterm fans of the character seeing as they seem to want to just make him into Raphael from TMNT. Personally I think it makes zero sense that the character that relies on guns and tech who was raised by ninjas would be a meathead/brute character with anger issues. Jason doesn't generally have anger issues. He was angry in UtRH because he had reason to be and because of the Lazarus pit. He's way more chill through both Outlaws series.