It's ridiculously cheap.
When Han killed poor Greedo he was doing it to save his life, his nonchalance made the scene cool and in the Wild West mode but it wasn't a cheap gag at the expense of a character the audience has invested time and interest in.
It was also a snap shot of Han at the beginning of his journey.
Fett is a broad-strokes mirror image of that Han.
A cool mercenary with a great looking spaceship.
It would make Han cooler if he let Fett live and didn't bother fighting him because he has changed or when paid enough money Fett would turn on Jabba because he hasn't changed.
This is the essence of saga over episodic drama. How the journey changes the character.
Han stops being a gun toting mercenary with no roots, he stops being Solo.
So many mostly American films (Bond has also doing this sort of thing for 50 years) seem to think the audience needs a vengeful death at the end of a quest.
Batman in the comics and the television shows keep the villains locked up most of the time. Batman in every film kills one villain as a blood sacrifice to the audience which cheapens the characters.
Star Wars was better than that until ROTJ.
Vader survived the Death Star battle not just because he was popular (nobody knew for sure that he would be then) not just to progress the story (the Emperor could have had dozens of nasty dark lords) but because it was cool not to tick off every box with a death. It would have been cool without a sequel, in the same way that killing Maul wasn't.
If the first act was expanded into a feature, just about rescuing Han from Jabba, I could imagine a scenario where Han's dismissive comments about Luke's training gain extra irony when he, blinded by hibernation sickness bests Fett using his instincts in a long drawn out duel in the desert. Double Noon on the Dune Sea. Even then I would probably let Fett live, not out of some fan love for the suit but because Han has grown to the point where he probably feels sorry for poor Fett who truly is alone.
In the current film Fett has no reason to be there and killing him in a throwaway showdown is just tacky ( stupid PT style slapstick in the theatrical version). He is just the first in a check list of characters Lucas felt the need to bump off in the last film and it just feels fake.
Fett, Jabba, Yoda, Piett, Palpatine, Vader, The Empire, it's too much for one film especially when it's shoe-horned in to tie up every loose end which never happens in real life.