Not one bit. If Maddison was deemed that good a premiership player, he'd have gone for more than he did - see Norwich now with the fees for Godfrey, Aaron's, Cantwell etc. He was a good enough risk to take that has paid off massively for that outlay. And I'm sure we'd have raised an eyebrow at paying £20mill for a championship player - like Villa spending £30mill on Watkins.
And I'd disagree to say that most thought Iwobi from Arsenal for £30mill was bad business to begin with as pointed out previously (he'd also scored in a Europa League final btw).
But your argument is that we should only spend low fees on potential, and higher fees on guaranteed buys? Doesn't work like that.