I actually found this really interesting, hard to watch at the start however.
One thing they seemed to say is it's very possible Kos could come back and be physically better off, maybe quicker, more agile, better power and that he should be able to get back to the level he was or even better. They also mentioned how this injury could actually make his career longer.
I wonder if they are 'just' saying this or they actually believe it to be true. I genuinely thought Kos probably wouldn't play 1st team again, but if we could have a Sokratis and Kos partnership for a year or so I could see that being solid while we wait for a top CB.
I only know one person who had an Achilles injury, and she came back quite the same, but then again she was rather slow and not agile to begin with.
In terms of ACL injuries I know people who didn't have it operated on when it wasn't fully torn and just built up muscle to keep the knee stable and it worked for them to come back the same, at least until they stopped being pros and thus stopped working on their muscles. So there's possibilities to deal with heavy injuries and come back well.
So it might be true, or not. Depends on the individual I suppose.