Increasing defense of noaml paras in unbalancing.
If they had for example defense of 12, who would build Infantry or use helidop???
Similar to modern paras. If you increse defense too much you outclass TOW Infantry, simple as that.
But, I must say that with current rules TOWs are excellent helidrop forces. And that normal paras are useful if you are smart.
You can, for example, support your Tanks that are advancing to enemy (by paradroping at Tank positions), and that way give them more defense (9 instead of 8). Similary, you could helidrop infantry to Tanks too, but helicopter can be intercepted by enemy planes, while paras can't.
Unfortunately this tactic doesn't work for modern paras since:
-Modern Armor has good defense
-Modern Armor has good mobility so doesn't really need defensive support
-Modern Paratrooper has weak defense, but weaker then TOW for example