Technically you are correct (the best kind of correct). But on a standard PC motherboard/configuration, DIMM slots are used exclusively for RAM which is much faster than ROM/storage. 3dxpoint was specifically marketed as being almost like a RAM/ROM hybrid in application. You could have 32GB RAM for regular computing plus 512GB of optane in the remaining DIMM slots and it would be like having swap space with very little speed penalty.

So GP is right to be concerned about speed for these form factors. If it's not faster than an NVMe drive them it's not worth the price.