MBAs are definitely great if you are switching fields. They are also great from a networking perspective.
There are plenty of people who studied business or marketing as an undergrad who have gone on to have successful PMM careers.
You can't stop competitors from copying your product messaging. That will always happen in highly competitive markets. But organizations can focus on building differentiated products.
Existing customers should be your product champions. You should be getting them involved in betas, cusotmer advisory panels and the like. They can help shape product direction and help you understand messaging that will resonate in the market.