I totally agree with you, and statistics in this case are only indicators, really.
And in this particular case, 100 + goals indicates we score a shitload, far more than any other team, but still we do not win the league. This tells me, that this call I see quite a lot here on the boards, for a "replacement" of Aguero (and Sane), is really not that big of a problem.
I don't see how we would prevent further losses next season by first of all making sure we sign a Sane replacement (for example).
But I would of course love to see us keep banging them in for fun AND have a better defense, and I fully believe that is what is in Pep's mind.