My background is in human medicine, and I have participated in FDA protocols, clinical trials, and data evaluation and peer reviewing, as well as having over 40 years in clinical practice in pediatric, orthopedic, medical, and surgical specialties, with additional clinical experience in mental health, nutritional and diet counseling, and physical assessment for health insurance companies, and over 30 years as a college/uni professor of medical sciences.
In my opinion, the studies on this are insufficient to draw conclusions that justifly the use of tongue ties. No one study weighs heavily, especially when only a few horses participated. There is valid research and not-so-valid research, but before condoning any practice that has not undergone the kind of rigorous evaluation required to earn approval under FDA protocol and having been determined to be both safe and efficacious, I don't typically support it.
When an effect from a drug or device is determined to be "clinically significant" the effects may be either harmful or helpful. Anything that impacts status quo for the worse or for the better can be considered to be clinically significant.
The FDA approves some drugs or medical devices without scientific evidence that clearly demonstrates why and how they work, but they are first studied under strict scientific protocol to determine that they meet minimal safety standards and that their efficacy is sufficient to warrant approval.
As far as answering the question as to how effective tongue ties are in preventing soft palate displacement, for me the jury is still out until long term, scientifically conducted, controlled, monitored, and validated research protocol is followed on a random and sufficient population to provide conclusive evidence.