It appears 300k is possible, but certainly not the norm for the majority of psych.
IMHO 300K is very realistic if you do private practice. The problem with private practice is it's not for everyone.
Why don't more people do it? IMHO it's because most doctors are hyper-specialized and don't know a lick about things like paying rent, managing employees, sitting down with the accountant, and worrying about someone shoveling the snow to prevent a lawsuit if someone slips on the sidewalk in front of the office.
Medical doctors enter a type of comfort-zone mixed with being a pseudo autistic-savant (indoctrinated by medical school after years of putting in inhuman amounts of data for years) where once they make something comfortable they really don't feel the need to do the job for the most amount of money. Things like being able to go home and not worry about work do matter.
I've done private practice and there are things about it that are annoying. If you work in someone else's private practice they may want you do to things you don't want, and if you own it, you got to worry about things most people don't in a institution such as the above. If you have employees that blow it can make life hell. I remember a buddy of my dad had a private practice, fired a secretary and she sued him for racial discrimination because he hired his daughter to fill in while he found another one. All the secretary could tell was this "new secretary" was of the same race as the employer and went racism-ballistic. Yes, the case was thrown out but the guy had to spend hours of wasted time and legal fees. Another buddy of mine was sued, not for malpractice but for violating someone's civil rights. The case from what I understand already incurred over 6 figures of legal fees and thankfully he didn't have to pay a dime because he's in an institution and they're covering it. Had this been private practice, he would've been SCREWED.
The benefits I get out of my faculty position are that I have colleagues that are literally some of the best doctors in the country. The atmosphere plus the ability to consult with them for emotional and professional support helps out. Further being in an institution allows one to exploit it's benefit and retirement packages. E.g. the institution will match what I put into my retirement package (right there that's about 20K a year), pay benefits, pay my malpractice, and when I'm off of work, I'm off of work. The place I'm at makes more money than most academic institutions I know of but they also force me to not be allowed to work elsewhere.