I'm sure both Aké and Cancelo are terrific leftbacks, but that's not the point. If we decide to not go for a leftback, then we have Mendy who Pep doesn't trust and we all know he won't be good enough this season. Leicester was just a hint of what's coming if we don't bench him. Then it's back to Zinchenko and he's not good enough either. Then it's either Cancelo or Aké, but then we are short on cover for Walker, Laporte and Dias. It's not a good situation. Aké is needed at centreback and Cancelo is needed as a rotation for Walker.
We have to get Tagliafico, or honestly anyone good enough to actually defend that area. 22m for Tagliafico is not pocket change but for his quality, it's nothing. Five full seasons with Tagliafico before turning 32 years old.