I am not to sure were that myth about copperslip has come from but it is a myth as far as I am concerned but it may be someone has applied the idea of galvanic corrosion between Al-Fe to Al-Cu. In theory this would be an issue but oxygen has to be present which the anti seize stops. Also your BB cup is steel which corrodes galvanicaly with aluminium and it alloys. So if you cannot use copper slip that was the case then the UN54 BB would never be fitted to alu frames which we do.
I think this is all down to font of knowledge/echo chamber that is the internet and the over application on the reactivilty/galvanic series. In reality it is not a problem.
Anti-sieze is just that for staic parts, grease is for moving parts. If you are really worried there is a aluminium based anti sieze. Grease will work though but will not last as long, which is why it is important to re grease your seat post regularly.
Oh by the way I have a metalurgy degree and teach Chemistry and Physics.