Mixing or blending diverse tile thinsets together
I'm hoping you haven't paid yet.

I don't think any manufacturer would consider this acceptable. (You could call their tech support just for laughs and see what they say.) At the end of the day, manufacturer's specifications are what matter.

So let's assume you have a sub-standard job. Off the top of my head, here's a few options:

1- tear it out and do over. (At the installer's expense.)

2- if they won't do over, on the premise that you didn't get what you paid for, pay them less. (Possibly a number approaching zero, given the risk of massive failure. If it went to court, I can't imagine that the installer would prevail.)

3- engage a different professional to fix everything and backcharge the first installer.

4- trust the installer when he insists that the job will be fine and functional. This approach requires that you actually believe you'll be able to find him in 6 months when the tiles fail.