People who work more get more done. Yes, there are limits. It's not obvious 45 hours a week is that limit.
Observe that the two places in the world with cutting edge AI startups are America and China. Europe has none. Maybe Mistral if you're generous, or DeepMind if you ignore that they got bought by Google, which IMO is OK because a lot of US startups have no plausible future outside of being bought and nobody claims that makes them not an AI startup.
But US and China lead. Americans work way more hours than Europeans do, mostly through taking fewer holidays rather than working Saturdays. And the Chinese have caught up to the cutting edge of AI very fast, despite facing trade sanctions, Great Firewalls and other obstacles. It is reasonable to infer that they did this by working really, really hard.
I was once told by a US executive that the rule of thumb is people in America (vs "Americans") work ~20% more than people in Europe. Skill level is the same, but Europeans both get more vacation time, have more national holidays, and are harder to fire for low performance. It adds up to a big difference, especially compounded over time. If 996 adds another 20% for China over America, then the Chinese will take the lead. They might burn out a lot of devs along the way (in fact they will), but maybe not as many as you think - after all America has not suffered mass burnout from having 15 days of vacation a year instead of 25 - and success will continue to accrue.
This is a painful truth. I myself work part time and get European vacations. It is pleasant. Yet I know it cannot last. Europe has become a vassal continent, in which Trump dictates terms and the EU accepts them without negotiation, because of the decisions its society has made; one of the biggest being to take life easy.