Your ally does not get your proficiency bonus to attack simply because you are not the one doing the attack. In fact you don't roll any dice.
I think the only thing i'd change about this power is that instead of "basic melee attack" it would read just "basic attack". I don't think it would break things up since you'd still need to engage the enemy in melee AND sacrifice your attack. Also, this could give some usefulness to those 2 ranged basic attacks (Eldritch Blast and Magic Missile).
And finally it would also mean that, in order for the warlord to be really effective in for the group he wouldn't need to stand on the Fighter's shadow all the time... (ie. most warlord attacks requires that you have an ally either adjacent to you or the enemy).
I think the only thing i'd change about this power is that instead of "basic melee attack" it would read just "basic attack". I don't think it would break things up since you'd still need to engage the enemy in melee AND sacrifice your attack. Also, this could give some usefulness to those 2 ranged basic attacks (Eldritch Blast and Magic Missile).
And finally it would also mean that, in order for the warlord to be really effective in for the group he wouldn't need to stand on the Fighter's shadow all the time... (ie. most warlord attacks requires that you have an ally either adjacent to you or the enemy).