If you stop thinking, then of course you will learn less.
If instead you think about the next level of abstraction up, then perhaps the details don’t always matter.
The whole problem with college is that there is no “next level up”, it’s a hand-curated sequence of ideas that have been demonstrated to induce some knowledge transfer. It’s not the same as starting a company and trying to build something, where freeing up your time will let you tackle bigger problems.
And of course this might not work for all PhDs; maybe learning the details is what matters in some fields - though with how specialized we’ve become, I could easily see this being a net win.