Prescribed Evenity after 2 years on Tymlos.

You’re not missing anything there really isn’t much solid research on the exact sequence of abaloparatide → romosozumab. Most studies look at Evenity either as a first treatment or after antiresorptives (like bisphosphonates or Prolia). There’s very little high-quality data specifically on switching from Tymlos to Evenity, so you’re right to notice that gap. What doctors are likely thinking (based on how the drugs work): Tymlos = purely anabolic (builds bone)
Evenity = dual effect (builds bone + slows breakdown)
So if Tymlos didn’t give much improvement, Evenity is sometimes used as a “next step” to try a stronger or broader effect — even though that exact sequence isn’t well studied.
From what people report (anecdotally), results are mixed — some see additional gains after switching, others don’t see a huge difference. It’s pretty individual. Big picture, the most proven sequence is still: anabolic → antiresorptive. Whereas anabolic → anabolic (like Tymlos → Evenity) is more based on clinical judgment than strong evidence.
So basically:
you’re right, the research is limited
your doctor isn’t doing something totally out of left field
but expectations should probably be “possible benefit, not guaranteed”
If you do go that route, it’s also worth asking what the long-term plan is after Evenity, since that next step is actually more evidence-based.