I really believe that perio is very misunderstood by some GP's and lots of posters over here on the thread that TX OMFS linked to.
For one, perio is a specialty where it matters a heck of a lot which program you go to. If 90% of what you learn is basic perio, hemisection, SC/RP, etc then that is what you'll do in private practice. There are programs where residents place 15 implants through the 3 years. Ridiculous.
Then there are prograns where residents place 100+ implants, do a dozen or so sinus grafts, and do plenty of ridge aumentations. Ridge augmentation requires learning autogenous grafting techniques (ie: chin, ramus, buccal shelf, tuberosity). To the OMS guy who suggested that OMS can do perio surgery if they wanted to..... well considering that the goal of most practicing OMS is to stick to implants and 3rd molars, do you really believe that perios could not overtake your surgeries if they wanted? Do you really believe that 3rd molar sx is more complex than a chin or ramus graft? Want the severely medically compromised pts, you can have them. Trust me, no practicing OMS wants them.
Perio spends a ton time learning how to avoid/blend gingival scar tissue, learning the fine points of very delicate esthetic cases. OMS does not. Do you think that there is no need for it? To suggest that OMS can do it just as well without the training is the same as the GP saying that they can do 3rd molars just as well as the OMS.
Anyways, I do believe that perio is very financially rewarding but it varies depending on what you do. There are single practitioner old school perio guys with 1 hygienist that make 150k. There are also guys that focus on implants and related surgeries that make 400k. There are group practices that have up to 10 hygienists going at once while the perios do graft after graft after graft and they make around 400k too.
Endo and ortho may be more guaranteed big money but each has their downside. The money is a tough question to answer because there are plenty GP's that earn 300k too. Just being a specialist doesn't necessarily mean more money than a GP. But it does make it much easier to get there.