Some of this information is misleading. Keita, Matip, Shaqiri, Milner, Gomez, Tsmikas, Henderson, Alisson, and Mane (though it was just dead leg) have all been out at some point this season. There's only been 8 matches in the league.
Sure, some of these would happen anyhow. Additionally, there's no question that there are other injuries that are not disclosed, and are more of the type like Mane had, with dead leg, or stuff that they're playing through. I'm also not going to argue with the fact that Liverpool has played a brutal number of matches. Especially over the last two or three seasons for many of these players. But, it's no shock that hamstring, thigh, muscle type of injuries are popping up with more regularity, and that's clearly due to the lack of a preseason, and the frequency of matches.
I don't know if 5 subs, as to 3 subs solves it, because Klopp and Pep didn't even use all 3 as it stood, but it would allow him to give a planned rest like he has in the CL to players. Give top guys 60 minutes. Pull 3 guys off if you're up 2-3.