"tested"? As in, played an STF for 30 minutes?
As one that has a gen7 longbowman alt, i can say that the only buff/change longbow needs right now is one that removes the sadistic upkeep from bodkin arrows. It is the sole reason, why i don't play my archer alt nowadays, i can't afford it.
Your "buff" would render the longbow unable to hit the side of a barn from medium range and far, far too slow to be able to actually do anything other than a single arrow at close range (and still have to pray for it to hit something).