Is jumping up and then placing a block before you can fall back down an exploit then?
Probably yes, but not to the same extent as waterbucketing underwater. Placing the block hardly makes any difference if you fall off a cliff. If you can survive underwater by pouring water above you into a bucket and then magically draining oxygen from the air which somehow appears, then it is exploiting. If you do it once when underwater, it's not very exploitive. If you abuse it to stay underwater so you don't have to worry about bubbles, then it is very exploitive.
What about using boats to levitate TNT?
Idk how you do that.
Fiah, sorry, I thought it was a typo, because the sentence made no grammatical sense otherwise.