1) Good job reenforcing Canon's customer-unfriendly design practices and rewarding them for their marketing rather than their actual products. You are why we're having to have these conversations at all. Stop giving companies money until you know that they've actually delivered.
2) Tamron's 17-35mm f/2.8-4 is lighter and smaller than this, also uses a 77mm filter thread, and at least going by Bryan's results of this 14-35, the Tamron is optically better in the center and only very slightly worse in the furthest corners. The f/2.8 wide end is a bit soft but you can consider that aperture to just be a bonus, since the Canon lenses don't have it at all; stop it down to f/4 or beyond and the Tamron sharpens up significantly. (Or at least my copy did.) I've owned the Tamron, it wasn't my favourite wide-zoom by any means, but if size is important to you then it is your winner and optically it's very good. I did prefer the optics of the Canon 16-35mm f/4 and that's ultimately what I stuck with, but I appreciate not everyone wants to carry something that size around (and it is only size, not weight; the EF lens is only 80G heavier than this RF and only 150g heavier than the Tamron!) and/or pay that much.
However you spin it, however you want to try to justify it to yourself, you know that you've paid a gigantic, arbitrary premium, twice, for the sake of saving 80g (180g, if we're including the adapter), about ~1.5cm in length, and a clearly-flawed extra 2mm which is being completed via software rather than the glass you've ostensibly paid for. This is the problem—you are part of it—and this is what manufacturers (it's not Canon alone) need to not be rewarded for.