Xeviat
Dungeon Mistress, she/her
But if Smite and smite spells both cost a bonus action, you couldn't do both.It would have the exact opposite effect.
A Paladin could dump a smite (and a smite spell) on a hit, greatly increasing the paladins nova.
At 5th level a Paladin could Smite (twice) for an extra 6d8 radiant and easily apply a 1st level slot for an extra 2d6 damage and knockback with a 1st level slot.
Removing concentration also encourages an active Hunters Mark or Divine Favour for an extra 2d6/ 2d4 damage as well. God help you when Holy Weapon comes online at higher levels.
'Bonus action on a hit' would encourage nova strikes and burning spell slots, not discourage it.