The squad Klopp inherited had finished 2nd one full season before. The season before he took over they had finished 6th. The squad Ten Hag inherited had finished 2nd one full season before (and reached a Europa League final). The season before he took over they had finished 6th. Quite similar.
As others have mentioned, Liverpool were consistently worse than United, finishing outside of the top 4 every season in 5 years except the title challenging one. That was an outlier; outliers are not what one builds an argument around.
It's not that hard to judge. You look at the players' track records, careers, etc. It shows pretty clearly that United's squad was better than Liverpool's.
The 11 most used players for Liverpool in PL 13/14 (when they challenged' for the title) were Mignolet, Skrtel, Henderson, Suarez, Gerrard, Johnson, Coutinho, Sturridge, Sterling, Flanagan, and Leiva.
The 11 most used players for Liverpool in PL 14/15 (when they finished 6th) were Mignolet, Henderson, Sterling, Skrtel, Coutinho, Moreno, Gerrard, Can, Lovren, Lallana, Allen.
The 11 most used players for Liverpool in PL 15/16 (when Klopp took over and they finished 8th) were Mignolet, Clyne, Can, Moreno, Milner, Lallana, Firmino, Lovren, Coutinho, Leiva, and Sakho.
As you can see from these "most used" lists, there are only 3 players in common from 13/14 to 15/16: Mignolet, Coutinho, and Leiva. 4 if you count Sakho (who was the 12th most used player in 13/14).