A .22 will train you on everything but the recoil, and save money.
Trigger time is almost always a good thing.
Even an airsoft replica of your chosen defensive weapon will help in practice for quick&dirty draw&fire on torso-sized targets, and be safer for you to practice your draw with until you have it ingrained into muscle memory. (safer for the neighbors if you insist on draw&fire practice at home, too!)
Obviously you can't do all your defensive training with a .22lr replica or "close enough" gun, but you can hone your; grip, sights, trigger press, draw, follow-through, and safe holstering with a crummy airsoft, a .22lr gun would be an improvement over that, and would let you focus on the recoil-related aspects when shooting the more expensive centerfire ammunition (that would be recoil control and follow-up shots, mostly)