I mean, tenta missles are really as effective as to how bad your team is postioned.
If you and a couple of your mates are holding hands together like a bunch of sissies, tenta missles is there to punish it, as your team just took a barrage of 12 missles heading for you. And in the confusion, you might suffer a couple losses. Typically though, if the tenta missle user locks on only one or two targets, the effect isn't that threating. Just run around in a circle or move after a little while when locked on.
Sure, getting spammed with tenta missles is annoying, but you should probably hunt the nerd who's spamming them if they're giving you that much trouble.
Tenta missle spam isn't nearly as annoying as ink armor spam though. Unless you want to lose every team fight to armor chaining, you should try and pick off the ink armor user themselves.