I'd say the lack of good coaches in JP is definitely a problem, but it isn't the sole reason why they aren't good. I definitely agree with what you said about their level of competitive exposure. But from what I've seen, JP teams make a lot of fundamental mistakes. Just using spacing as an example, they often are positioned too far apart to effectively trade off each other, taking a lot of unfavorable 1v1 aim duels, so they throw a lot of rounds despite man advantages. Or they'll play way too passive and not take map control to gather/deny info or bait utility. They'd show a lot of improvement if they got good coaches to fix a lot of these fundamental mistakes and provide structure for these teams