WOW - that Canon 28-70 f2 is a pig - guess it isn't a DO lens... 95 mm filter size? That's larger than most 100-400s, and larger than any 70-200 f2.8 I'm aware of. The only lenses I know of that use a 95mm filter are some of the Sigma x-500mm zooms (maybe the Nikkor 200-500 as well)?
1430 grams? It weighs almost exactly as much as a Canon 70-200 f2.8 (the latest IS III version), or the Nikon equivalent, and about 150% as much as any 24-70 f2.8 (they're mostly right around 900 g, Canon's is a little lighter, and the Sigma Art is a bit heavier). Why build a lens like that for a mirrorless camera? Especially as one of the first few lenses available? If it sat on top of the EF normal zoom range, where there is already a 24-70 f2.8 and a smaller, lighter f4 option, it would be an understandable lens... It might actually balance on an EOS-1 series body...
We have one body, and it's roughly a 6D mkII equivalent. How many people even use the trinity f2.8 zooms on their 6D mkII? I bet most of them are paired with the f4 lineup, unless they are backup bodies to EOS-1Dx models (or maybe 5D mkIV). Why build an exotic lens (and this is unabashedly exotic - I bet it's over $3000) for a single midrange body? Especially for a body whose advantage is mobility?
Of the first four lenses, we have a reasonably sized 35mm, a fast (but big - right around 1 kg) 50mm, this monster and a 24-105 that is reasonably sized for what it is, but perhaps not the first choice for a compact mirrorless body?. Nikon got this aspect right (at least in terms of specifications) - their first lenses are compact and lightweight, supposedly with excellent image quality - we'll see. Fuji has always gotten this right.
Stop thinking mirrorless = small. That was 8 years ago, and that idea has probably held back mirrorless development and uptake more than anything else.
Yes, you can make mirrorless systems and lenses smaller than SLRs, if you sacrifice sensor size (M43), aperture (f/4 zooms or f/1.8-2.8 primes) or lens image quality (UWAs without a retrofocus or telecentric/near-telecentric design). The lack of a mirror box and pentaprism reduces the lower limit on size. But just because you can doesn't mean you should. Small size comes at a performance cost; if you want a more capable lens, you're going to have to go bigger. You
can make a lineup of slow pancake lenses for the 'small camera' niche, but that is just a niche (albeit the easiest one to capture with the sluggish, slow-focusing early mirrorless cameras which really couldn't offer much else other than small size) and can't/isn't/won't be the primary target for a camera company trying to take mirrorless mainstream as an SLR replacement.
Many people shoot mirrorless - particularly full-frame mirrorless - for reasons other than size and weight. Those focusing on small size are shooting M43 or Leica anyway, or have a Sony body with a few pancake lenses; they are not the people currently using 5D4s and 6D2s who need to be encouraged to move over to mirrorless. Mirrorless allows for an EVF with through-the-sensor image preview (including exposure and colour settings), better video performance and (on cameras with the right hardware/firmware) features like IBIS, eye focus and other AI-based focus modes. There are many photographers out there who would choose a mirrorless body even if it were the size and weight of a D850.
The 28-70/2 is a perfect event photographer's lens. It covers most of the useful focal lengths for indoor and small-area events, works better in dim lighting and produces more subject isolation than a 24-70/2.8 and weighs no more than the 70-200/2.8, which is almost permanently attached to one of a wedding photographer's two cameras. Combined with a mirrorless body and a decent flash system (the Sony flash system doesn't count as 'decent'), it provides additional capability no SLR does. Event photographers can repeat many shots (posed individuals or groups) but only have a few seconds to do so (groups won't stay posed for half a minute while a photographer chimps, adjusts settings and re-shoots). They also commonly shoot in JPEG, due to the need to quickly produce a large number of images and prints for collection at the end of the night. EVFs offer real-time white balance, exposure and image processing (saturation, contrast, etc.) previews, making them far better for shooting JPEGs than SLRs, no matter the lens attached. The 28-70/2 on a mirrorless body is almost ideal for this kind of situation - and this kind of situation represents a significant number of Canon SLR users. Just turn up to any corporate or social evening function and look for the photographer carrying a 5D3/5D4 with 24-70 and flash attached. A mirrorless body with 28-70/2 does the same job, but better.
Canon didn't release a 24-70/4, and Sony/Zeiss didn't update theirs, because they already have a 24-105/4 which offers a much less limiting focal length range for the single kit lens user. The Sony 24-105/4 G is optically very good, and there's no reason the Canon one won't be too. And they're not dramatically larger or heavier than a 24-70/4.
