Sigma’s ‘modern’ 14/1.4 is twice the weight and far larger than Canon’s RF 14/1.4*.
Yes, and for astro (which is what the Sigma is specifically designed for) the Sigma is by far the superior lens, while being 30% less expensive. If you want a lens for video on a gimbal, the Canon is the right lens and the Sigma would be ridiculous if not impossible.
Question I’ve asked several times that no one has ever answered: Canon RF has a set of three full frame zooms that cover 15mm to 400mm for under $1700, what 3rd party or other OEM kit can cover that range for that cost or less?
So, from Canon we have:
RF 15-30 f4.5-6.3 IS STM at $539
RF 24-105mm f/4-7.1 IS STM at $459
RF 100-400mm F5.6-8 IS USM at $699
$1697 (current prices on B&H)
On E mount you can get:
Tamron 17-50mm f/4 Di III VXD at $599
Tamron 50-400mm f/4.5-6.3 Di III VC VXD at $1199
$1798 (current prices on B&H)
So, the Tamron pair is a hundred bucks (6%) more expensive and 2mm narrower on the wide end. However, they are actual legit premium lenses, both of which have extremely fast magnetic linear drive motors. And there's only two of them which means less lens swapping and less to carry.
The Canon lenses meanwhile are decidedly entry level, have much MUCH smaller apertures, and two of them use slow STM for AF. On the plus side, while the f7.1 is IMO atrocious, 24-105 is a convenient daily carry range.
I would take the Tamron pair every time as the Canon glass is just too slow (both in aperture and STM...) I suspect if the Tamron glass was available on RF, many RF users would make exactly the same choice. Of course, they are not permitted to have that option.
One could also argue that lenses designed to be smaller, lighter and cheaper by incorporating digital correction into their design are more modern than lenses that are larger, heavier and more expensive than they need to be in this current era where the lens output cannot be seen optically, only digitally.
I'm not personally against corrected lenses. Sony does it too, and it makes sense. It's really the Nikon fanboys who freak out about it the most, but the trade-off is that their lenses (especially the f1.2 primes) are HUGE and very expensive. IMO it's not a good trade.