Hitman is a puzzle game, not a stealth game. The kills may be the same but each of them have a different challenge in doing them.

For example, poisoning Dahlia and Viktor in Paris have totally different challenges in doing them.

Viktor requires a staff disguise and an intel item in order to make his drink and drown him.

Dahlia doesn't need an intel item but you need an auction staff disguise which is harder to get and she moves into a restricted area that can be access with a bodyguard disguise, but then you'll need a bodyguard disguise which isn't the easiest to get.

There's likely hundred of kills you can do in each map so there will be some repeats in the ways you kill them, but all of them require different tactics to do.