Yes, because one person completing a contract using coins totally RUINS someone puzzle. Like total destruction, no coming back from that. That one person ruined the entire contract for everyone untill the end of time. Because that is how it works. Because logic. Such ruined, much destroyed.
I have done more difficult and challenging things in this game than you ever will by a longshot.
It also opens up possibilities for new stuff that would not have been possible without it. Like the flying haybale. The haybale argument alone is already more than enough to counter any argument you will ever make.
And it doesn't ruins puzzle. It takes way too long in almost every scenario.
If i would make a truly complicated contract no amount of coin luring would help anyone. Even with coin luring it would never become easy. If you think otherwise you are wrong.
It resulted in the haybale kill, which is one of the most memorable ones. And yes that was fun to watch.
Breaking this game is a form of solving the contract aswell. Just because you don't like/understand that does not make it any less true.
Oh and yes, HITMAN is most definitely a puzzle game