My opinion is that there is an advantage for privates, however there is no known way to "correct" it. The best correction which already exists are the OHSAA recruiting restrictions. The general myth is that privates recruit, yet how many complaints or challenges were filed with OHSAA in the past 3-4 years on recruiting violations? A handful, and none were actual violations.
One thing that acts somewhat as a balancing effect is that public schools in effect give "scholarships" to every kid who walks throught door - i.e., free tuition and books. Privates can cost any where from several thousand to over $25,000 per year in Ohio.
I'm not going to go find the posts, but on JJ Huddle's men's soccer forum, about 8-10 months ago, someone did an analysis of all three divisions, back to 1999, and ranked them for the entire tournament outcome. The public schools ranked highest in all three divisions for how far they went into the tournament. What was however not considered was the number of public schools vs private schools (i.e., if private's are 20% of the entire pool, yet rank at the 40% level, is that an issue). The post was not about privates vs. public but about ranking programs over the time period based upon tournament outocme.
Many states have a multiplier so that the student population of schools who can admit students outside the district is multiplied by a number, such as 1.5. This can force a school into a higher division. Most states who have adopted this system apply it only to private schools, however some to both private and public if the public has special programs where students from different districts can attend. The many studies done on this system show the multiplier "solution" does not have an effect in the real world environment (i.e., at the 1.5 to 1.8 level, it does not have a statistical effect in changing the outcome). No state has looked at different multipliers for different sports, but just one for all. Further, apparently no state association has the stomach to go above 1.8 (it leads to the question of how many public students are equal to one private school student, which is a political issue noone wants to deal with).
OHSAA has looked at the multiplier several times, and last Summer briefly adopted it before turning around in several weeks and going back to the old system. Don't know why OHSAA did that, but the rumour is the football coalition killed it.
Some states has a separate tournament system for privates and publics. One even has a separate system but the final is against the winning public and private. I think separate tournaments in Ohio might kill OHSAA (which I beleive is an excellent organization). It would likely lead to a new OHSAA type organization for the private schools, so we would never have a true overall winner in a sport since both systems would likely have different rules.
While the current system may not be the "best," my opinion is that it works and I would not be in favor of changing it.