I didn't say Greizmann was like Mata and Mikhitaryan. Indeed, Mata and Mikhitaryan differ from each other too. I was using trequartista as an umbrella term.
United don't need Greizmann for goals having just spend £75m to £90m on Lukaku. It's a matter of supplying Lukaku, and the midfield contributing goals to supplement his tally.
Regardless of their playstyle both Mata and Mkhitryan are playmakers by trade, Griezmann is not. Also saying we don't need goals because we bought Lukaku but then saying we need more goals from other areas of the pitch makes no sense. We absolutely do need more goals, signing one of the World's best finishers will help us in that regard.
Claiming we shouldn't get Griezmann because of Mata and Mkhitryan is similar to claiming that Mahrez is the same sort of player to them both too. Just because they can occupy the same positions doesn't mean they don't offer things the other players don't.
Besides - Griezmann is no slouch in the playmaking aspect, he'd be working both off and with Lukaku, feeding balls into him and running onto balls from Lukaku as well. He'd be an immense signing for us and would replace Mata in the team.