The classless system is not truely the case for PoE though.
Even though everyone can get the skills that they want to, it still makes sense to go for a specific class build because of the ascendancy classes which make classes feel rather unique as you said.
I do think that in Diablo should not strictly go as far as PoE does and every class should represent what they actually are meant to, but the freedom of build to allow characaters to use other classes spells does not hurt anyone.