not sure about that, feeney and astley have both shown they could cope with the physical aspect of lower league football. they just weren't good enough to play higher.
I was at a semi pro v amateur friendly last Saturday and remarked you could see the difference in physical size between the teams , and I think this is replicated as you go up the leagues. The size can be there in League 2 but there are are other aspects like speed , subtle aggression combined with strength which make a difference higher up the league. Astley or Welch couldn’t cope with Kane for instance he’d outmuscle them , unlike
Tarkowski who’s better able to cope. ( I know there’s a huge difference there in ages and capabilities of Tarks compared to Astley/ Welch) . Conversely I think it’s one of the reasons Simms struggles more in the PL , he can’t bully defenders the way he does with “ less physical “ defenders in the Championship/ League 1.
Size isn’t everything of course in a defender , but it’s more and more a determining factor and may just be such a factor in how far ISS progresses .