Quite right that it's not sustainable and is vaguely absurd; however, that is modern football.
Seems a bit like entering a casino, losing an absolute fortune betting on bad hands etc, and then afterwards saying "You know, this whole gambling money to win money thing, it's really quite silly. We don't do that."
Well you do, actually. You've thrown away crazy money on average players for years, and based on the most recent window, that's still more or less the transfer policy. That goes for both Toon and Villa, for the record.