My feeling on training to land a single, balanced attack is that it only ends up being useful in a strictly kata situation. If you look at the top boxers - only the really top guys have a connect rate over 40%, for most boxers (even good ones) the connect rate is much lower. If you rely on that one attack then you've got less chance of connecting then if you just flipped a coin.
It works the same if you're giving or receiving - if you only work against that single balanced attack then you're training yourself to work against something that really doesn't happen very often.
Fine for Kata training of course.
In terms of the mechanics - I feel strongly that strikes have to come out of the same basic body usage as everything else.
I am not talking about "relying" on it at all. And I am not even saying you only get one of 'em. I am mostly saying that working on combinations and jabs and such does two things: takes time away from learning technical basics, and moves you into the realm of sport fighting.
What are you saying doesn't happen very often?