I accept some of that, but the central thrust of Keane's point seemed to be about protecting the younger players. One or more of Shaw or Stones or Phillips (or Pickford!) would very possibly have missed as well (although Shaw scored a penalty in the Europa League final shoot-out) but, according to Keane's line of thinking, had any of those missed they'd be better equipped to deal with the aftermath of missing than Saka or Sancho. (Another point: Italy had a defender and a defensive midfielder among their first five takers!).
Saka at 5 was the only really contentious one for me (although I do have issues with Rashford and Sancho coming on just for a penalty having barely featured all tournament).
Keane's point (as we've now found out) was misguided, as it was Southgate's decision to put Saka a) in the 5, and b) at 5. Swap Saka out for Sterling or Grealish and I don't think anyone has any issues with the 5 nominated takers.
Saka taking at 7 behind those two wouldn't have raised anyone's eyebrows, really, given he's considered an attacking player, and I think we'd have heard far less about it had he missed at that point.
I agree with the general line of thinking that the older, more experienced players are more equipped to cope with missing the decisive penalty, but you can't just put the youngest player last, and you also can't expect every player to be up for taking a penalty. Keane probably struggles with the latter more than anything, because he prides himself on being a one man winning machine, and can't wrap his head around a player not wanting to step up and win the match for their team.
Italy's nominated takers are neither here nor there for me. You pick your 5 out of those that say they're up for taking them and order them accordingly. Perhaps a number of the Italians weren't really up for it.