No the Focal length argument applies to any lens on a DX camera
There is no 50MM DX Lens, because it would not be 50mm, the 35MM DX lens is essnetials the same as 50MM on a Full Frame/Film Camera. DX lenses are optimized to completely fill the Smaller sensor of a smaller DX camera, where if you put on a Full frame lens, doesnt matter if its 50 years old or came out today, some of that light comming into the lens spills over outside of the censors view thus having less viewing angle then if it were on its proper frame.
There is nothing wrong or bad about using a full frame lens new or old on a DX camera, just need to be aware that the focal length will be more then what the lens is rated for. Even with DX lenses, while they are optimized to fill the DX censor properly, are not exact
And as I said, i was not 100% aware of this myself until i read into it, but you said yeah exactly “agreeing” with my post when thats not at all what I said