In general, I don't like this idea, but I think there is a way to do it that BENEFITS Xbox and INCREASES users joining the Xbox ecosystem, rather than driving them away.
Further, by the games MS is talking about moving, it does fit with this strategy.
It goes like this: if Xbox ports older games in existing franchises to PS (note that GoW 6 and other new titles are NOT on the list to migrate), then PS players who would otherwise not be exposed to those games other than by reviews on the Internet and maybe occasionally seeing them at friends' houses, have a chance to play them. If these experiences are positive, then some percentage of those players may buy Xboxes for the latest versions of games in those franchises.
The key requirement for this is to ONLY give the older versions of the games to get them interested in the franchise, keeping the latest and greatest exclusive to Xbox (or at least ensure a significant delay before releasing a new version to PS). This makes PS players always tardy to those franchises. If they care about the franchise, many (not all) will want to be able to get the best versions of the games.
The logic to this is clear: expose more people to franchises, get them interested, then they may convert to Xbox from PS either immediately or in the next generation when they upgrade.
The counter-argument is that just as there is a portion of gamers who will want to get on Xbox to play current versions of the franchises they like, there is also a portion who is happy to stay a version behind and will figure with PS they get all the PS exclusives plus are ONLY 1 version behind on the Xbox games too. What we don't know, but MS might, is the ratio of these two groups. If the eager players group is as big or bigger than the happy-to-get-all-exclusives-even-if-years-later group, then it's a good strategy. Otherwise, it could be very bad.
I would caution MS that the damage caused if they miscalculate this is severe. Some experiments and tests are low-risk, easy to win back customers (e.g., putting out a game late loses some sales and delays revenue, but if it's good, customers come back), but customers who move to another ecosystem may never come back, or at least not for multiple platform generations.
So I can't say if MS' plan will work or that the positives outweigh the negatives. I don't know if they do. But it is a valid strategy that might be better in the long run even for Xbox hardware sales.