1. OK, that resolves why you are wearing them down , and I can only strongly advise that you change your diet completely ASAP or you will keep having problems. Maybe you would benefit from the support of a dietician. Some dental schools have them on staff too.
2. Oh, so the Invisalign has left them unable to touch with the lower teeth? That's bizarre and short-sighted; it's not a good way to handle this problem. If you went to a prosthodontist I would expect them to be similarly aghast at the treatment you are receiving. Some people think we shouldn't criticise our colleagues, and sometimes that can be true because I don't have your full history etc, but I hate to see laypeople given limited and harmful options.
3. Composite rehab would aim at restoring the lost tooth structure on ALL your teeth (front and back) in the most conservative fashion. Crowning your teeth is an aggressive treatment. Sure, you might add a bit of length, but you have to grind off the front and sides of your teeth. Comp rehab is done simply adding to the length with MINIMAL tooth damage and minimal risk. Crowning is non-reversible; comp rehab is mostly reversible.
4. Question: How can you bite through food if your front teeth don't meet?
Answers: Either (a) you still are biting with your front teeth by sliding your jaw into an accommodating position, or (b) your front teeth are slowly growing back into contact again (the Dahl Concept), or (c) you are now eating more on your back teeth so they will start to wear down instead. All of theee possibilities are bad for you.
5. There's a saying, "Give a carpenter a hammer and he'll want to hit a nail." This narrow thinking also applies in medicine and dentistry for many people. Partly due to our limited training. One only gets to think outside the box by going to lots of seminars, getting lots of experience, and (sadly) working in this game long enough to see what happens to long-term health of our patients when we offer poor choices.
Case-in-point: 2 days ago I was teaching in the student clinics and a patient like you came in. The student could only think in terms of what their limited knowledge told them, so I sat down with student and patient and gave them nearly the same long talk I'm giving you. I wasn't taught any better in my training, but I'm not going to let the next generation of dentists make the same mistakes I made. It may not be that the dentists you are seeing are just looking to do a quick fix at your expense; it is more likely that they simply don't know any better.