They look just fine to me .. any thinner and they may look like children
I know its not completely responding to the topic here, but I think I these positions need tuning as a whole rather than just certain players:
Halfbacks: They simply aren't meaty enough, they need much larger lower bodies, and their frame needs to be a lot thicker. A lot of them look like receivers to me.
Receivers: The powerful and aggresive ones need to be a lot thicker, for example TO or Anquan Boldin, these guys are 220-230, they don't look much bigger than guys that are 190 in my opinion
.. Is it possible to have a "thin, built, thick, huge" kind of frame related system, and be able to edit our player's proportions from that? I think that would solve a lot of people's issues with what someone is built like