Given that KensaiKensei Monks are forced to take a ranged weapon as one of their KensaiKensei Weapons, we can assume that KensaiKensei Monks are intended to be reasonable ranged attackers -- I believe Deft StrikesStrike exists mostly to support that. Most of the other ways to spend ki at level up until level 11 either require (stunning strikeStunning Strike, flurryFlurry of blowsBlows) or are most useful (dodgeDodge/disengageDisengage) in melee situations, which most bow users try to avoid (and monks would be generally better at that with the +15ft movement they'd have at level 6).
Deft Strike allows a ranged KensaiKensei Monk to spend Ki to increase their damage. Seems a welcome option. Allowing melee monks to use it for the few situations where immediate guaranteed extra damage is helpful is just icing on the cake.