I agree with that.
Looking back and Arsenal probably got Sanchez on the cheap considering what he has done since joining them, finding another gem like that for the £35m they paid for him is hard. It was the same with Liverpool and Suarez.
If we get Sanchez that significantly weakens Arsenal. If we do keep Aguero, to have him Sanchez, Sane, Sterling and Jesus as attacking options and that should seriously rival what the likes of Madrid, Barca and Bayern have to offer going forward.
The great thing about all those 6 players is that they are not fixed to one position, only Aguero is really an out and out position player as a main striker.