The issue is not tabs vs. spaces. It is block indentation vs. alignment. If you use alignment you are forced to use monospace fonts, if you use alignment with tabs, everyone is forced to set the same tab-stop (missing the point of tabs).
Block indentation on the other hand allows people to use whatever font they want (including non-monospace fonts) and what ever tab-stop they want. At that point it doesn’t matter anymore whether the indentation is done using tabs or spaces. The preferred font settings of the developers can deal with it.