I mean on Williams, I'm not sure he did look that good. I am not slating Ireland, but they are in essence a championship level team and he looked comfortable. Thats his level really. When he played in the PL, he's been badly exposed, and it's telling Klopp's preference was to play Milner, a 35 year old midfielder at right back ahed of him.
As for the squad, they are fortunate they didn't manage to move on the players they wanted too. They actually had quite a big squad, but filled with decent players on massive wages. Obviously the more injuries they get, the more pressure it puts on. Matip should really only be played 1 game every two weeks if they want to get him through. Probably the same as Gomes. They've been ran into the ground though by Klopp.
Some of the injuries they are getting are problematic too. Hamstrings are a nightmare to get over, and as you say, medium term really hinder you. I remember Mirallas for us, who went from being top draw to really being a bit of a liability once his hamstring went.