Slow aircrafts have such as A-37 has been used for COIN roles for a long time. IMO if we must go for an old aircraft, why not rejuvenated and modidfied A-37s’. PAF has been using T-37's for the last 50 years; hence training/support infra structure is already in place.
A multi role aircraft by definition is a compromise; therefore an aircraft built for a specific role will do a much better job. Besides for COIN work; why would you use J-17 when you can
have a squadron of A-37 for the price of single J-17,
As long weapon systems perform the task, age of design is of no importance. For example, Lee Enfield 0.303 is a WW1 vintage rifle. I have used it myself, it is still a cheap, sturdy and reliable weapon and in good hand, suitable for sniper work and static defense.