Don't listen to a practitioner that blames your body or that even tries to convince you that your health issues or challenge are just because of a longer leg. It is not true. Maybe it contributes but your structure isn't the guilty one, you are not.
Health, life, joy, the manifestation of any symptom doesn't appear only because of one variable, in this case, a longer leg. Psychosocial health, nutrition, movement, rest, work, postural habits, emotional state, life purpose, will power level,... Everything affects and influences your health and it wouldn't be fair for you to identify yourself with one not perfect attribute and give away your power to someone else, therapist or not.
Maybe it would be more fair to say that a longer leg can create a compensation in your hips and spine mechanics, which can make your system less efficient. Actually I have found that most of people's legs aren't longer or shorter, it's just the loading over the years that has created compensations in the tissues of all system, including feet arches, all connective tissue in the body that connects through the hips, so most of it, actually. A flatter arch can bring the inside of the knee closer to the mid-line and make a difference in both sides' adductor muscles group, which will alter the height and rotation of the hips, for example. All these can make your system less efficient and more prone to have specific restrictions, which will impact the system in various ways. Always different in every one of us, so an accurate assessment and static and dynamic postural analysis will be the key. There are many ways to address these issues, being some therapies more passive and others more active, requiring different levels of participation and involvement from the client. Not so many are integrative and include and empower you to go through healing with learned lessons in a body level.
Statements like those can harm people and "manifest" or "write" another suggestion results than the one that truly empowers you, affecting the present and the future, as such as some few dishonest, unconscious and manipulative future tellers. There are genuine ones as well, even though this post isn't about that.
I have met so many clients that deeply believe this precise statement and, no wonder, they often have low back pain! Because they have a longer leg! When analyzing their whole system I realize that maybe 1 out of 8 has longer bones, but it's all about the connective tissue and muscle compensations, as a matter of fact.
Be your own master, be open for opinions and new approaches, but only the ones that empower you and give you tools, that include you in your own healing process. If not, leave that therapist, because maybe they believe too much their own "story". Don't settle for less. Quality over quantity. Results are always subjective, depending on what you give importance to, your core values. For the rest, here we are. At Postural Patterns we do talk about longer legs, but in a context of globality, functionality and integration. What matters is the function, and not so much the structure. In the process, the efficiency is optimized, posture changes and awareness increases.