>>The problem with MBAs is that they are often too expensive / not the right fit for startups, not that they have limited career prospects.
MBA's are best suited at places where you need things to be generalized and managed even if it is at the expense of efficiency.
If you are looking at hard focus based work which requires a lot of application of specialized knowledge and effort. MBA's not just make a bad match for those jobs, but will likely mess it up.
You need MBA's when you need some super abstracted generalized knowledge applied to non critical tasks. You can hire an MBA to run a hospital's billing unit, but not to treat patients. Same with software and start up's. You can use them to do some work on stuff like market research, setting up the pay roll unit, attendance systems etc.