Well, Liverpool's recent success (tough to call it a true success with one trophy won, but ok - they'll get the Premier League this season) is strongly related to Klopp getting pragmatic and being able to spend large amounts of money on established players, on contrary to what he was claiming when he first arrived to England. Van Dijk is a good example of that kind of transfer - they payed above the odds for him and never looked back, as he proved to be such a monumental signing for them. Keita and Alisson were both 60m+ deals as well if I am not mistaken, Fabinho costed as much as what we payed for Fred.
Yes, our players seem overpaid for how United is playing these years, but let's not have an illusion that more successful English clubs are paying less for their players and dominating due to multiple successful ca. 10m transfer punts that worked out wonderfully. United is not the best place to develop recently, and without true leaders in the locker room, on the pitch and among the management, it's not that easy to reach your full potential. I think players like Grealish, Fernandes, Sancho or to a lesser extent Koulibaly are precisely what we need - established players, ready to step in and instantly improve first team but still with a room for development and hunger to win their first relevant trophies.