Well, the title is a bit strange. People are poking fun at PHP, I do too - but ... if PHP were totally useless, nothing would be affected as nobody would use it. But many servers use PHP and there is good software written in PHP too. I know that because when servers were patched, and taken down, a lot of stuff suddenly no longer worked. That included universities as well as some other websites. So I think the term "technical debt" is strange. PHP is written in C. Would PHP be better if written in Rust? That's not so easy to answer, but all things being equal, it may be that PHP would have fewer issues if it would have been written in Rust.

I think one should, of course, be critical of those who write C code for PHP, but at the end of the day, some part of that criticism also goes to C. C is both a king and a problem. And it seems very hard to fix the problems of C.