I think its kind of spot on actually... it gives the extra attack .... but its a big picture extra attack a "controller" style extra attack in 4e or a leader style one right out the gate. Instead of the single target fighter smashem variety.A variant Extra Attack might go something like: Whenever you take the Attack action on Your Turn, you can make a second attack against a different target, or give an ally advantage on their next attack against your first target.
While a maneuver might go: "When you use Variant Extra Attack to give an ally advantage against an enemy you attacked, that ally can use his Reaction to attack that enemy, immediately." or "When you use Variant Extra Attack to give an ally advantage against an enemy you attacked, that ally gains temporary hit points if his next attack hits." etc...
...meh... it's a thought, not sure it has much potential.
That is actually better than my first parse of it makes it. Hey @doctorbadwolf did you examine this idea. Cake and eat it too.