And there's the rub. Migraine as a cause for dizziness is only a theory. It's a popular theory and has become medical dogma, or "flavour of the year/decade". Previous owners of this crown were 'Menieres' and 'Perilymph Fistulas". And notice how they were very careful to call it "migraine associated" not "migraine caused".
We should all be very wary of dogma.
I think the reality is a lot more complex and involves inner ear dysfunction. Sure, of course there are neurological elements to the issue. I believe that the migraine process and the nature of the root cause (my bet is on a degree of hydrops). may be preventing compensation. The drugs help calm the neuro transmissions and aid the compensation process by helping to block the brain going into some kind of electrical spasm.
But nevertheless there is a change in the vestibular apparatus due to some lesion or injury for which a compensation is required but more difficult to achieve because the issue fluctuates. On top of that I'm very sure the acute vertigo episodes are not migraine as I've had full on spinning vertigo whilst on prophylactic meds and off them. They only helped prevent me vomiting not from feeling a spinning sensation. My money is on something going on in the inner ear during those episodes.
What I wouldn't dispute is that the medical treatment is reasonable. But as another clue to the complete story note that people diagnosed with Hydrops and fistulas also get the very same meds because it helps them. Very suspicious if you ask me. And if we keep backing the wrong horse there will be less investment in research into the ACTUAL root cause. It's sad to say but the treatment is a very convenient 'take this and you'll feel better" and let you go home and deal with it ... And for years on end!! Who wouldn't want something better than a nebulous theory?!?