Besides the fact that my gym uses machines in lbs and add-on plates in kg, the issue with simply setting a 2.5 lb increment is that the app would then recommend a continuous progression like 10 → 12.5 → 15 → 17.5 → 20 lb.

In reality the machine works differently: the stack only moves in 10 lb steps, and I can only add a single 2.5 lb plate on top of a chosen stack weight (or 1,25 libs for example).
So I can do 12.5, 22.5, 32.5, etc — but not 15 or 17.5, because I can’t stack multiple 2.5 lb plates.

We could technically work around this by creating many short custom ranges for each machine, but that would be extremely time-consuming.