

Looking at this with adult eyes, no I don’t think you’re a jerk. It sounds like you’re trying help him see the reality of the situation before it causes him any undue emotional (or financial) suffering. It’s not, however, very hard to imagine how from his point of view he might feel like you’re being jerk, or maybe a bit hypocritical.
Is there any way you can get him playing with kids who are good enough to go pro? If he can start playing against people who genuinely have the goods, it’s probably not going to take him very long to figure out for himself whether he can keep up or not. And that way you don’t have to set yourself up as the bad guy as much, and you can play a more supportive role and be there to guide him to an alternative path once he gets sick of the other kids running circles around him. At least that’s how it worked for the couple of kids I knew growing up who were good enough at basketball or American football that they really thought they could go pro. It was playing against people who were the real deal that made them realize they didn’t have the shot they thought they did. It was pretty obvious that these other kids had something extra, and were playing on a level my friends felt they were probably never going to reach.
If the process and tradition of it appeals to you, then sure. You can find a cheap matcha set for under $20 (I think I saw one on Amazon a while ago for $10), so it’s not like you need to spend a ton of money to try it out.
I’m kind of lazy so I use one of those electric milk frothing whisks instead of a traditional bamboo one. But if you use that type of electric frother just be sure to use it in a vessel with high sides and a fair amount of extra room otherwise you’ll be wearing your matcha instead of drinking it.