It seems you may have misunderstood what I said. I said that down the road he might top out at A HIGHER LEVEL. The implication is that H3 could force him to fix some of the inefficiencies that are causing him not to translate power into the ball on contact and that would mean that, RATHER THAN THE RUBBER DOING THE WORK, HE WOULD HAVE TO HAVE BETTER TECHNIQUE. So your: "Or not. He might be ending up with a forehand much more deadly than any of his clubmates." is a different way of saying just what I said.
Because you do have to translate more power into the ball, someone with poor mechanics who keeps using H3 and trying TOO HARD could be more likely to end up with a shoulder injury. Because Catapult sponge makes it so you do not have to work as hard, and medium impact shots have what most people would consider good power, someone with poor mechanics could potentially just not try as hard with Catapult sponged rubbers which could cause the bad mechanics not to create the injury as quickly.
Someone with really good mechanics can get a HIGHER TOP END POWER with H3 while, with Catapult sponge rubbers, at a certain point, more effort stops producing more power (speed and spin on the ball).
But still, all sports have the potential to cause injury. Good mechanics make you less likely to injure yourself. And a person can injure themself no matter what equipment they use.
So, I would not say "for every H3 user." I would say, someone whose mechanics are good enough that the transfer of power from legs, hips, core, and arm, into the ball on contact is effective and efficient is less likely to injure themself no matter what equipment they are using and someone whose mechanics are less efficient might work harder, get less power, and then try too hard and injure themself no matter what equipment they are using. But a rubber that makes the ball go faster when your mechanics are not quite as good could make you use less effort. That could make the less efficient technique a little less likely to cause injury. But it is the technique that would create the repetitive stress that causes the injury one way or the other. And if the technique does not get cleaned up, over time, the poor mechanics are still likely to cause injury. It may just take longer to manifest with a rubber that does more of the work for you.