I mean, you're talking like Mane, Gini, Salah and Firmino went for peanuts. They didn't. They went for 25+ a pop. That's their entire budget on two or three, and then some in one window.
The only low margin purchases Liverpool did were Milner (Free), Matip (Free) and Robertson. The first two, they had to pay absurd salary and pretty much give a better opportunity to get done.
I'm not saying they can't go out and get value for the money, they certainly can, but it's not as easy to say they can go out and buy 60 million of players (more likely what they'll have to spend) without saying who they could have bought in 20-20. I agree with your principal, that there is value to be found, but what's to say they're going to be the ones to find it? Who is actually even in charge of getting value in transfers?
(I also would hesitate to say that some of those 'hits' are hits yet. There's a lot left to prove that some of them can get better, or can do it more than one season.)
I also think there's something to be argued that Klopp and Edwards now have a bit of a track record to where if Fabinho failed, they're not getting sacked. If Keita doesn't come good, Klopp isn't getting sacked. Could Emery afford to pay 30-35 million for a player, have him flop, and Arsenal be able to pay for another just like it? Would Emery have the rope to miss the CL, and not succeed with transfers?