If I can't you as well can't prove that some of his reactions are faked or exaggerated.
I mean, if you have been watching his videos you'll know that he loves with passion games such as Final Fantasy VII or 3rd Strike, or that he's super fan of characters such Rock Howard. Knowing that his super positive reactions to anything FFVII related or when he saw that Rock was in the background of Terry's stage makes a lot of sense, and this is only to name a few examples.
Obviously each people expresses his emotions in a different manner, I'm not a guy who would jump or scream like crazy because my fave character is in Smash, that doesn't mean other people can't be more expressive when it comes to videogames.
Also, usually is pretty obvious when someone is faking a reaction only for the sake of getting views. Max doesn't give that feeling, and if he's really faking his reactions then I'd say he's an incredible actor lol