Putin and Zelensky are both legitimate military targets, so is the Kremlin.
There will be cost associated with this attack and does nothing but escalate an already disastrous situation. It probably for the time being stops any efforts to negotiate a settlement.
In WW II, the allies decided not to attempt taking out Hitler, because it would unite the German People and Hitler’s military decisions were insane and it was better leave him making decisions than to take him out and risk a competent leader taking his place.
The same thing could happen with this attack, any Russians on the fence about this war are now probably united with Putin. If Russia and Putin are incompetent and he was taken out in a drone strike, what are the chances a new Russian Leader would not be far more ruthless and insane as Putin
I fear this attack only escalates into a really dangerous situation that ends with consequences no one predict.
Taking out the leader of a strategic nuclear power a major escalation to be sure - if it’s ever successful, certain things could be nearly automatic in progression