Yes, You are right but have a look at the dimensions and compare a Sigma 12-24 f/4 with this lens:I don’t know, one stop is a lot. Otherwise why bother getting an f2.8 rather than a 4. Or a 50 1.4 rather than an f2. I could go on. Yes, one stop is a lot.
Sigma φ102x131,5mm , Laowa φ69.4 × 74mm That is a lot!
Sigma 1150g, Laowa 497g That is a lot!
And this does not include the EF-RF adaptor.
If You have to carry the lens for a few days on a hike the difference would be a huge advantage.
But of course the Sigma is an ART lens and the Laowa has also to compete in IQ.
Laowa still has a 10-18mm f/5.6 lens with E-mount and it's IQ has not convinced me (I don't own or have used one, but the pictures I'have seen on the homepage and reviews).