But to tell someone to tone it down? No, that I wouldn’t do. They mean it sincerly, and the truth is, we really SHOULD be davening like we’re on fire, so I think you did the right thing by not saying anything
My right to swing my fist, the saying goes, ends at your face. Likewise, the young man in question has a right to daven with as much fervor as he likes, but his right ends when he disturbs other people and prevents them from davening. To paraphrase the gemara, who says his davening is sweeter to HKBH’s than the OP’s? As such, I believe that, in theory, he should be made aware that he is disturbing others and asked to tone it down.
I say in theory because I don’t know the entire situation. It’s possible that, in saying something, he won’t change anyway (or, if he’s perverse, just “up the ante”). Nor do I know if the OP has the option of moving or not. In short, the OP has to do a risk/reward analysis (perhaps speak to a rav he respects for advice?) on whether or not to actually say something.
The Wolf