I don't know why I'm playing Devil's advocate,
maybe I got out of bed the wrong way but here goes again.
I think the fixture congestion is more about maintaining the teams highest levels amongst all the players during their real fixtures especially with players carrying injuries etc. In friendlies you can step back off the pace and make it more relaxed, and also you will get injuries no matter what, look at Tommy Smith against Real Betis, it was a complete joke of a tackle by him that led to his own injury and really set the tone for injuries in the season just going out.