Watch Dusan Tadic tearing it up for Ajax.
1. If you are comparing a player by player:
1) Tadic is somewhat fast and can run past his opponents, Griezmann can't
2) Tadic can dribble, Griezmann can't
3) Tadic is 1,81 and can offer more physical and aerial presence in a box. Griezmann is built like a 13 years old for a No9
4) Griezmann isn't a lethal finisher at all
5) only things which Griezmann can do are: link up play, defending and workrate
Regarding Griezmann, there is an also chance for "Atletico's effect" where every majority of midfield and attacking players from Atletico look better playing for Atletico than in new clubs or NT teams.
2. That was an individual player vs player level.
Regarding a team, Ajax, they again have (a good manager, a good system, a lot of young and motivated players, but also): Tadic as a CF, two wingers around him and Donny behind him.
That means: even if Tadic will struggle with scoring, they will have 3 other finishers to step in.
Barca?
If you bench Suarez and play Dembele-Griezz-Messi, what do we have?
Messi can score.
Griezmann will score once in 3-4 matches.
Dembele is hot and cold.
If you add Busi-Arthur-Frenkie midfield without a CAM, we are even in bigger problems in terms of scoring if Messi gets injured or gets heavily marked.
Griezz seems like a good guy and a very good player for counterattacking teams as a deep lying-creator-second striker.
For our team, who plays a slow possession around the box, he is a horrible LW, and for a CF, his skills and numbers are way too low for us to rely on him and to consistently win matches.
Another mistake by Barto and his team of sporting directors.