Usually, members of editorial boards of journals are outstanding and experienced researchers (although there are exceptions). Independently of their role as a member of an editorial board, their papers are of high quality, otherwise they would not have got recognition in the scientific community. I would expect that their papers are rarely rejected. But I guess no statistics about the acception or rejection rates for editorial board members are published because such data are not publicly available, and the editors will hardly do such statistics.
TI would expect that journals would vary widely in this area. Some have lots of articles from editorial members, some would have very few. I suspect they would all be legitimate but there is a perception of bias, unfortunately, and it is probably better for those people to avoid publishing in those journals because it might be bad for their own reputation and the journal's reputation.
The acceptance rate of papers submitted by members of an editorial board to their own journal can vary widely depending on several factors, including the journal's policies, the quality of the submissions, and the integrity of the editorial process. Generally, reputable academic journals strive to maintain rigorous peer review standards regardless of the author's affiliation with the editorial board.
While there may be anecdotal instances of bias or favoritism towards editorial board members' submissions, reputable journals typically have mechanisms in place to prevent such conflicts of interest. This can include double-blind peer review processes where the identities of authors and reviewers are concealed from each other, as well as editorial policies that require board members to recuse themselves from decisions involving their own submissions.
It's important to note that the acceptance rate for any journal, including submissions from editorial board members, can vary widely and may depend on factors such as the quality and relevance of the submitted work, the competitiveness of the field, and the journal's editorial priorities.
Ultimately, the perception of how easily papers from editorial board members are accepted in their own journal can vary, but reputable journals strive to maintain impartial and rigorous peer review processes to ensure the quality and integrity of published research.