Except neither of those 3 play in the position that Jose wanted Perisic for. It seems he wanted Perisic as he could play as LWB or LW. Whilst for a LW you can make an argument for another style of player, for LWB it is much more restrictive. That would mean Jose now has to choose between a LWB or a LW. He could go for a LW but that tramples on Martial, or he could go for a LB. The LB position seems harder to fill overall.
Perisic seems to have been a good fit because Mourinho felt he could cover LWB (if Shaw can't play there) or he could play LW.
The haters for Perisic on here generally want us to buy a Dembele or similar style inside forward, because lets be honest they are flashy and exciting, however that leaves us with shaw or Darmian at LWB and whilst Darmian is an OK LB he definitely doesn't seem cut out for an overlapping LWB to give width. I know he played there in a couple of games, but he is a fish out of water.