What do you mean? Inzaghi always rotates by position. Whenever Hakan is not playing he plays Asllani. He isnt a 6th midfielder. He’s the only regista back up.
I mean in terms of minutes allocation. Obviously Inzaghi sees each backup midfielder for a specific position. Frattesi for RCM, Asllani for regista, Klaassen/Sensi for LCM. But in terms of minutes allocations there are clear hierarchies among our backup midfielders. As things stand Asllani is our 5th midfielder right now and that's where it gets problematic to sign a quality experienced backup regista.
While Inzaghi rotates defence, wingbacks and occasionaly even attack he rarely rotates midfield. Hakan has started all Serie A games but 3. Same for Barella. Mkhi has started all but 1. So the chances for our backup midfielders to start games are minimal. It's a bit better in CL (mostly for Frattesi) as Inzaghi chooses to rotate in group stage but it doesn't really change the general perception.
Then it goes down to their minutes from the bench. Unless an emergency occurs Frattesi usually is the designated first option from the bencch. Then it's Asllani and lastly Klaassen/Sensi. 1127 minutes for Frattesi, 707 for Asllani, 290 for Klaassen. That's for this season.
Now we're going into next season with Barella, Hakan, Mhki, Frattesi, Zielinski and Asllani. Whether Zielinski or Mkhi gets starting spot it's certain they will both get lots of playing time. Frattesi will also get significant playing time as he's a scoring threat and a big investment. That leaves us with Asllani as the last option in terms of minutes allocation.
And that's where the problem with signing a quality experienced regista starts. A quality veteran doesn't have the luxury to wait like a youngster does. He needs to play now and he expects guaranteed playing time. We have no way to promise guaranteed playing time to another midfielder when there's so much competition. By loaning Asllani out you risk ending up with a Klaassen type of signing who is just grateful to be in the squad.
It's easy to say let's have 6 quality midfielders. I would like it too. But it isn't realistic. There isn't enough playing time for all. You will just end up with an unhappy player in the dressing room.
I have seen this club having no Brozovic backup for years with the exception when Conte used Eriksen for a short period there and in the last few matches last season when both Hakan and Brozovic were available. I don't want to see it again even if it means having a backup whose ceiling isn't really high.