> Security? MUCH worse.

This is patently false. It is much better for security if you use one of the many memory-safe implementations of it. This is like saying “SSL is insecure because I use an implementation with bugs”. No, the technology is fine. It's your buggy implementation that's the problem.

XSLT used as a pre-processor is obviously also a fundamentally better model for security because... it's used as a preprocessor. It cannot spy on you and exfiltrate information after page load because it's not running anymore (so you can't do voyeuristic stuff like capture user mouse movements or watch where they scroll on the page). It also doesn't really have the massive surface Javascript does for extracting information from the user's computer. It wasn't designed for that; it was designed to transform documents.