To sum up the conclusion of many other threads on this subject (and similar subjects): good luck.
As a brief aside, there is a significant difference between something being "evidence-based" and "standard of care." Plenty of things that are taught in medical school don't actually have any clear literature support for their practice, but continue to be practiced in the absence of evidence refuting their use. For one example, until recently aspirin was used routinely for heart disease (and colon cancer) prevention across wide swaths of adults. These recommendations were finally changed in 2022 when relatively new randomized clinical trials were able to show that the benefits may not outweigh the risks unless a patient has specific risk factors:
USPSTF Recommendation: Aspirin Use to Prevent Cardiovascular Disease . These trials were able to be conducted because they were of great interest, the cost of running these trials was very low (basically any patient can buy aspirin over the counter for negligible cost), and the practitioners could easily have "clinical equipoise" (i.e. believe that it is equally likely that treatment with aspirin or not would be beneficial, thus making it ethical to randomize patients). It still took a tremendous amount of work to change the standard of care.
Bringing this back to your question, I think it should quickly become apparent why these OMM principles are unlikely to be removed from osteopathic education any time soon--you're almost certainly never going to see a RCT that is going to address the question of chapman points to "disprove" their use. Frankly, with relatively few physicians using chapman points and thus relatively few patients being impacted, there would be little interest in conducting such a trial. And further, the physicians who DO use chapman points in clinical practice likely lack clinical equipoise (cynically, they may even feel incentivized NOT to participate in a trial that challenges the practice in standard of care). So in the absence of such new RCT data you are unlikely to see the teaching in school change.
TLDR: you're not going to change anyone's mind on the standard of care without clear evidence refuting the use, so OMM is likely to remain part of the price of admission to DO schools.