Now I’m not knocking osteopaths generally, as I know a lot of people find them helpful, and you obviously have faith in this one.
BUT, it’s still in the category of “alternative medicine”, and he is no way qualified to diagnose that your disease is “progressing”. So frankly, I wouldn’t set a lot of store by what he has to say, and it certainly doesn’t mean you’re progressive (as in SPMS).
Having said that, everyone’s MS “progresses”, anyway. It’s an often overlooked fact that even RRMS is progressive. It doesn’t mean: “Fine when not relapsing”, even though that may be true at first, for some people. But does your osteopath actually understand the difference between progression and a relapse? I very much doubt such subtle distinctions come under the umbrella of osteopathy. If you are in, or have recently had a relapse (which is implied by the fact your neuro wants to switch drugs), it is normal for your symptoms to be worse. It’s not necessarily “progression”, as there may still be complete or substantial recovery.
So I would put what he said from your mind - an osteopath is not the best authority on these things.
I’m not saying don’t use alternative therapies, if you find them helpful, but do bear in mind that these people are not qualified to make clinical judgements about MS!