In restorative dentistry/prosthodontics, there are many different clinical philsophies, not just in prosthodontic programs, but also CE courses. When you sign up for a residency program or set of CE courses to learn FMR, you are subscribing to their particular brand of clinical practice. Finishing a whole series of CE courses or a residency doesn't mean that you are done. In fact, it is only the beginning of your career-long (hopefully not lifelong) journey. As there are strong/weak prosthodontic programs, I am sure there are strong/weak CE programs as well.
I'm an advocate of doing more than just what a specialty can limit you; If I were to place 28 crowns and I had to do 10 endos, I'd like the option to do the endos, CL, osseous surgery, etc... That's the advantage of doing CE and working in private practice simultaneously. You practice the way you want to practice and make way more money with less restrictions on your autonomy. The only questionable aspect is that your first cases that you are implementing your knowledge on, are pretty much your guinea pigs. However, the same can be said about a residency (although you have a faculty member backing you up), if you have a good friend or paid a prosthodontist to fix what you've messed up, it's essentially the same thing. I guess what to choose all depends on your learning style. If you like to take a course, implement what you've learned and learn from your mistakes as you go (and make more money in the end), then private practice + CE is the way to go. If you prefer to have a more structured learning environment with more variables under control in the academic setting, then go to a residency.
Now, for the timeline. The timeline depends on the length of the residency program v. CE courses (series). Why would you need to be stuck in an academic setting the whole time unless you're allowed to moonlight, make money on the side, AND implement what you're learning, then that makes a lot more sense. Unless, of course, you're stuck doing labwork or non-productive procedures that a DA/CDT/MDT/MDC can perform.
If you want to focus on cosmetics, there are plenty of CE courses out there that cover from photography all the way stacking your own porcelain. You don't need a prosthodontics program to do cosmetic dentistry. IIRC, there are some cosmetic dentistry residencies, but I'm not sure if there are still any operating at this time. I had an opportunity to work with a few of the residents in dental school. You must really love cosmetic dentistry to dedicate that much time into it. It's almost an obsession (but in a good way, if you enjoy it).
I like the CE route if I had to choose. I have the ability to learn in progression, without taking a bunch of my time, apply what I'm learning in my own practice after that session is over and in the context of owning/running a practice. You have a front row seat of seeing what works and doesn't work in the real world. In a residency, it's more insulated.