Yes but when you combine it with the other guarantees on performance.

https://github.com/google/cel-spec/blob/master/doc/langdef.m...

And your service puts an upper bound on input size and cel expression size. (True for all practical applications.)

You can actually get a guarantee tha t you can't construct a billion year expression. And even guarantee that all expressions will evaluate in let's say 60 secs.

Turing completeness by itself does not guarantee this but it is a necessary prerequisite for these guarantees.