While they used to be fine, they were rebalanced to be batshit op. Keep in mind the stock okw has effective no weakness mainline AND core elite long range elite infantry so a unit that has infiltration built into its cost can't compete. It's similar to the problem with elite infantry in the usf. It's difficult to make a doctrinal unit that is technically not needed be attractive.
So a balanced infiltration unit will seem worthless (as both jli and falls seemed to the powers that that be)
It is all about making a unit bring something different to the table.
JLI could easily remain an infiltration unit if they pop, CP and power level was reduced. They would still be useful as scouts.
Fallj could easily remain an infiltration unit if their design to be closer to commandos probably cheaper with lower power level. They have little reason to be an airdropped unit and the problem with over lap remain there regardless of method of entering the field (airdropped or infiltration). Actually they could do both in their old implementation.
There is no reason for OKW to have both of their infiltration units removed.