I agree that having a lower-powered system to undercut the competition is good strategy. I also think requiring games run on it in a rare feat of MS standing behind its hardware is a solid choice, even if it does carry some negatives for games that struggle to run on it. The solution to that is to increase its market share so it's not an afterthought, at least until they move on to the next generation.
However, to Phil Spencer's broader point that rather than focusing on game advantages (exclusives), he wants to win market share based on hardware, that's inconsistent with MS' strengths and proven abilities. Unlike Nintendo, who took big innovative risks and won with both their Wii and then Switch, MS cannot innovate in gaming hardware. It's a demonstrated cultural weakness of the MS team. They tried with Kinect and failed. Since then, they've moved further from that (think Windows Phone, Band, etc.). Granted, those are not gaming systems, but the MS cultural problems appear to be consistent across the entire company, meaning they come from the top.
In defining strategy, success comes from finding ways to better leverage existing strengths and clever ways to avoid weak areas. MS' strengths are in its first-party game development, its possible tie-ins with Windows, its backward compatibility, GamePass, and possibly some others. It's weaknesses, especially now that it has lost much of its hardware innovation and engineering team, include its ability to create consumer-desired innovative hardware and now its perception of abandoning everything it starts -- this is a real liability. To bet on both of those over leveraging their ability to put out strong exclusives is just bad strategy.
Sometimes companies get lucky on bad bets, because sometimes chance rewards the lottery player, but that doesn't make it sound strategy.