It is very hard to troubleshoot issues without steps to reproduce…
All azerite powers stack if you have multiple of them (at least in all the tests/reports we had on beta).
We do our own calculations for the value of all azerite powers, trinket procs, etc. I can’t speak to the quality of the icy veins rankings as I have not looked at them or their methodology.
The optimizer certainly should not recommend removing your heart of azeroth, so if you have a case where it is, give us steps to reproduce and we will fix it.
Lowering item level by 100 in a slot should pretty much never happen either – if you can give us steps to reproduce that odd result, we can take a look as well.