The tnt kit is absolutely fine in my opinion, yes it does destroy the defences, it makes a decent hole, but you can also get the builder kit to repair that, you can stay at the core and defend it too, just because your defences are broken means that it is game over...
If ever this actually was a problem, I'd probably make the tnt kit more distinctive like giving the player a TNT hat or change the color of its armour to red... otherwise, I wouldn't change the kit.
Not locking the thread as there is no need to. The thread is still open for discussion.