All good questions that have been asked many times here. It all depends on how you want to practice. I would say that MOST if not all dentists and specialists chose dentistry for the autonomy, lifestyle and ability to open your own practice. Working in a Corp as an employee is a job. Nothing more. Nothing less.
After 26 years of private practice .... I currently work as an employee in a Corp office mostly as a way to SIMPLIFY my life. But I am on the tail side of my career. It's different if you are just starting out. For myself .... working in a Corp setting is SO STRESS FREE. I show up. Do my work. Leave. That's it.
Yes ... the Corp chains are encroaching on EVERYTHING. The Corp practice I work for has EVERY specialist there. After going to a Corp meeting .... I listened to their CEO discuss their future plans. They are going after Pedo practices now. They are buying them quickly. So the Corp chains are here to stay. I envision the large Corporate Dental Chains gobbling up all the smaller, less capitalized chains. It's already happening. Consolidation.
As for working for a GP/Specialist in their office? Not for me. I didn't go to DS school to work for another dentist, but that's just me. It's unfortunate that it has come to this IMO. Back in the day .... you earned the trust of the GP to treat their patients. Now the GP's want a cut of that referred revenue. If this was a rural area where you had to travel to a remote town .... then I could understand working out of a dentist's office. But I would rent or share space with that dentist.
In large urban popular cities ..... saturation will be commonplace. It's in these saturated areas where the private practice model will have the hardest time.