I don't doubt that Aguero is way past his prime and may turn out to be a huge flop (even Moussa Dembele has been a big flop).
But surely he is coming because he is a top finisher and good at finding half a yard in the box, has excellent technique to get a shot off from a small chance. Compared to Braithwaite and Dembele.
I think for weak opposition or moments when we need a goal then he can be useful. Obviously if he is coming to be an undisputed starter then that would be a very unintelligent transfer. But it is more than likely that Laporta is looking for a Larsson-eque move. And in that frame you only have a choice of Aguero or Giroud.
This is the point really. Outside of Messi and an injured Ansu, there is a lack of clinical finishing or killer instincts up front. You need goalscorers, Leo cannot be left with the burden of doing everything
Kun hasn't missed anymore matches than Suarez over the last few years and while Kun is only a year younger, his success on the pitch is less predicated on the collective play that Suarez often was forced to play without true wingers. That will not be the case with Memphis, for one, but either Collado/Dembele/Ansu on the other flank. Kun only needs a moment to release his shot attempts and while less versatile than El Pistolero, he has the burst/acceleration/strength inside of 5 meters that few forwards have in the game
He comes on lower wages than Suarez and knows the country & league very well - he should hit the ground running, provided he is healthy. Ultimately however, I think he is simply plan B - he serves purposes as a bonafide goalscoring threat to rotate with a 1st choice #9 (Depay or other) and he has more time to work on his chemistry with Messi ahead of the WC
Free, is always good - 3 incoming players who will absolutely compete in the rotation of minutes to influence the success of next season, none of whom will be arriving on exorbitant wages.
That leaves money to be generated from player sales to pursue a primary target (Haaland or other)