patwerthman, I'm curious about the source of your virtual recommendation.
I don't have experience with the medications except Forteo. Bisphosphonates are now recommended for three to five years. Because you haven't gained density with alendronate over the last year, it's a great time for the switch. I have a preference for Forteo because it is a lower dose of medication than Tymlos and because I'm not content with the mechanism of action of Evenity.
There isn't a way of determining how much bone loss aledronate has prevented. You probably have and will maintain fracture protection for several years from taking it, even as your bmd remains low.
In your situation, I would take Forteo or Tymlos for two years. Prior bisphosphonate use is said to delay the effectiveness of either medication, studies have shown that there isn't significant difference after one and two years of use. There isn't actual rebound with either Tymlos or Forteo. There is gradual bone loss after you quit using either drug.
I'm starting a third year with Forteo. At 16 months the T score changes in the spine were from -3.3 to -2.8; femoral neck -3.0 to -2.9 ; right hip loss from -2.4 to -2.5. The trabecular structure improved reducing fracture risk in the spine and the hips.
The endocrinology response surprises me.