I understand that avoiding spending a week on Y is important for business value, but constantly prioritizing shipping features in the cheapest manner possible also means not investing in the long-term growth of your developers. You don't learn much of value by gluing together a handful of framework functions. You become a better engineer by really struggling with and digging into Y for an entire week. If engineers are never given the freedom to do that, they stagnate as framework glue monkeys. "Deep work" is a rare thing in scrum shops.
That's a really good point. I know my career has nearly entirely been steered from "non-core" activities that I undertook which never would have been justified on a week to week schedule. Businesses also are actually very poor at understanding technical opportunities which developers at the coalface can see (that is, things that are technically easy or at least feasible, possibly due to the specific skill of the engineer(s) in question, but have very high value).
