I think a lot of the high functioning people who use THC could probably be even better without it. But what THC does is quiet a negative inner voice that prevents them from focusing and/or causes them to procrastinate. So the overall effect seems positive in the short term.
The issue is that THC does have long term effects. Most of which can be countered by being above average prior to use. Even if it zaps a few IQ points, being productive is better than being even smarter but paralyzed by anxiety. But the positive effects only last as long as the euphoria.
Some people encounter worse anxiety in the long term. A drug doesn’t solve the problem, just alters brain chemistry. Often the problem is external, rarely completely internal. If the initial source of anxiety is external, THC is a poor long term solution.
THC also does mess with reward mechanisms. Why feel good for being productive if you can just feel good by getting high? Without external motivators it’s easy to lose your internal drive when happiness is just a puff away.
It can also hurt emotional control, which is more subtle that other issues. That inner voice that causes anxiety is similar to the one that says slow down and be a nice person. By shutting one off, you also shut off the other. The same inhibition commonly associated with creativity is also associated with being a dick. THC seems to be associated with love, but this is largely a fantasy. Euphoria is not love by default.
I think the story about the productive stoner is over inflated. It’s a lot of work to truly solve the issues that THC can address. So if you are already high functioning, it’s easy to use a drug than address them instead. The issue is that THC will erode you over time, and may exacerbate the same issues that THC is supposed to address. Moderation is well and good, but the people using daily are self medicating, not using it recreationally. It takes a lot of control to not let THC take over your life when used regularly. And if you have that level of control initially, couldn’t you exercise it to live an equally fulfilled life in abstinence?
It’s difficult to even be recreational now that everything is so high potency. It’s like every drink being high ABV, and it’s an arm race to make it higher. Edibles are about the only way to ensure a low dose. As someone who prefers to smoke I find it next to impossible to match an inebriation level similar to a light beer, unless it’s literally a single puff. A second can send you over the edge.