Even if your crumbled concrete is what is called gypcrete or another lightweight substrate, successful installations can be done by a competent tile installer.

Perhaps this is a candidate for Schluter Ditra tile isolation membrane underlayment. Does your tile contractor know what Ditra is? Google it for information.

I am not a big fan of floating floors for lots of reasons, although some people love them.

Properly prepared with the right floor patch/underlayments can allow you to install almost any flooring product on your substrate...you just have to know what you're doing.

I agree. Schluter's "Ditra" will uncouple the floor from the tile.