I disagree. Every club makes mistakes even us who very well run like Liverpool. I could flip that and say they got 40 million for an ageing Fabinho, let go of Milner and Henderson and paid under 120m for 3 quality midfield players, which ultimately won them the title this last season. Other clubs like Chelsea are paying 200 million plus for less quality.
Salah and Van Dijk are well worth the money they are being paid. Those types of players aren't about in the market anymore, and they're still at the tops of their games as shown last season. Trent I agree with, huge mistake but they probably thought Trent would always sign a contract. Possible arrogance on their part.