In a practical sense, hasn't type theory already replaced ZFC in the foundations of math? Lean is what working mathematicians currently use to formally prove theorems, and Lean is based on type theory rather than ZFC.
Have you considered working at any of the national labs (LLNL, LANL, ORNL, etc.)? When I worked there I knew a lot of former armed forces members who had learned interesting scientific or technical specialties. It’s just an idea, in case it piques your interest. Most of the labs would be happy to have a motivated employee who is also interested in concurrently getting a college degree. PM me if you’re interested and I can try to provide more detail.
I had a friend in grad school who entered the Ph.D. program after spending four years in industry. He was very passionate about his research area, persistent, a fountain of ideas, and wonderful to talk with. He ended up winning the ACM doctoral dissertation award for his thesis, did research and teaching at a university, and has since returned to industry.
This may be the exception that proves the rule. However I just wanted to point out that there is at least one person who did catch up to become a research scientist, however rare that career path might be.
I don't think there is a clear-cut answer, but rather some pros and cons, which you're already weighing. I'll just pass on some helpful advice that I got, and some of the things I learned while doing a Ph.D.
- A Ph.D. opens up two things: (1) ability to do research, and (2) ability to teach at a university. A Ph.D. makes more sense if you really want one or both of those things. If you're already involved in research at your company, and want to go into the same research area, what a Ph.D. offers is the ability to continue doing research in an academic context. There are a lot of benefits to working at a university (the profs I know really appreciate academic freedom), but I also hear persistent complaints about funding and how difficult it can be to find.
- Choice of advisor matters a lot. A great advisor is a very influential mentor, who will help you grow intellectually in very many ways, and help you make connections to other researchers. A bad advisor can be really destructive. You need to put a lot of effort into evaluating your top several possible advisors. Which of them do you like? What are their former students doing now? (All of their students, not just the most successful.) What are their research groups like? What can you learn about the advisor from their students? If you were as successful as their median student, would you be happy?
- Some departments have more cooperation, some are more competitive. One of my friends ended up in a department that was ridiculously competitive, to the point of students excluding and undermining each other when studying for qualifying exams. She didn't like it and left after getting a master's degree.
>I joined a really cool team
Don't underestimate the satisfaction that can come working as part of a great team. There are no guarantees that you'll be able to recreate that on demand at a later point, or that the research group you end up joining will be as good (though who knows? it could be better).
Also, I'm sure you've looked into this, but is there a possibility of doing formal research work at your company (taking classes towards a Ph.D., finding an advisor at a university to oversee the academic side of your research, etc.)?
One lab that regularly tests for heavy metals, albeit in dietary supplements rather than spices, is ConsumerLab [0]. Their detailed findings are behind a paywall, which is unfortunate, but probably necessary for them to provide the service. And there is little public funding in the US for testing food for heavy metals.