They probably weigh the same, but today's players carry far more muscle. Most old school players gained pure fat throughout their careers and lost their athleticism like crazy. Today's players put on weight in a controlled manner, no sacrifice of skills. Jimmy Butler for example is in the 240lb range, last do ented at being 238. LA, last do ented at weighing 280. Even guys you don't think of as big such as Harden are pushing 230 which was MJ's weight at his biggest. I don't think there exists anymore 190-210lb SF's which were all over the place in the 80's n 90s, at least none that can actually defend.
a perimeter oriented game also makes the court bigger, more square footage players must cover on defense, and their offensive game usually consisting of ball handling which requires you to constantly stop, start, balance and contort your body also puts a lot of stress on the joints.
Players don't move like this anymore, that's for sure.
6'9 250 in yesterday's game, HOF'er Unseld
6'9 250 in today's game, Julius Randle
There really is no comparison, very very very taxing on the body when they're pushing weight at speeds like this.