I made no such implication. Mozilla is certainly an other party, and their positions on standards hold water. They successfully argued for Web Assembly over Native Client, and have blocked other proposals such as HTML Import in the Web Components API. They are still a key member of the WHATWG.

The fact that Mozilla aligns with Google on both of these deprecations suggests the reasons are valid.

I personally see no reason for XSLT today. Outside of the novelty of theming RSS feeds, it sees very little use. And JPEG XL carries a large security surface area which neither company was comfortable including in its current shape. That may change based on adoption and availability of memory-safe decoders.