Sancho is 3 years younger and homegrown. There's always a premium on young English players, otherwise it's like comparing Grealish's transfer to a potential Tielemens one when everyone knows it won't be anywhere near half the dosh.
I don't think anyone should be looking at the corrupt Pepe transfer and using it as a benchmark for anything, either. At very best, it's like saying any midfielder that isn't rubbish should cost more than Ndombele, just because Ndombele was £50m and turned out rubbish.