So you don't like the concept of "look, this is how you do it!"
or "Hey, he's leaving his left flank wide open." *whack* "See?"
It's something of a timing issue in these cases, since in between the leader's turn and an ally's turn you might very well have the turn of the creature whose "weakness was just exposed," and that creature can't do anything to
undo the bonuses the leader has given the allies.
If the sequence of events goes:
Leader: *smack* "He's open!"
Monster: "Apparently I am open and can do nothing about this!"
Party Member: "He's still open!" *smack*
....yeah, that breaks me out of the fiction of the game.
On the other side, the leader granting an attack with a bonus at that point doesn't really break the fiction.
Leader: *smack* "He's open! Billy, wail on him!"
Party Member: *free action smack* "Great! I have taken advantage of an opportunity!"
Works just fine.
It gets weirder when things like temp HP or healing or saving throws are involved.
Leader: *smack* "Because I stabbed that guy, you can try and throw off that poison, Billy!"
Monster: "Rargh!"
Party Member: "Um....okay..."
It's a problem with specific power mechanics, not an endemic problem to the system at all. Which is lucky, so that when I play, I can avoid choosing classes and powers that have that weirdness.
Though this is why I have trouble playing warpriests and artificers, since a lot of their powers key off of attacks that buff for some reason.