alright I did some extensive testing over the last 14 or so hours and documented it here.
Long story short is on 25.04.2.5, even with smartd set to “Standby” - it doesn’t let the drives sleep properly. What works for me is disabling the SMART service daemon (and preventing it from starting on boot). This is distinct from disabling SMART on your drives (which you want enabled).
I found this related GitHub issue - hope it gets addressed soon - looks like they could use a hand on this front.