So they also do a 150-600mm Contemporary model, which has 90% of the performance. It doesn't have full weather-sealing, and it has a different element arrangement which slightly changes the picture quality, but it also drops a huge chunk off the weight and about £400 off the price. It's not quite as solidly built but for a lot of people it's more than enough and provides a good alternative.
In my personal experience Sigma lenses tend to be heavier than Canon for equivalent build quality. ~10 years ago I'd say the picture quality was slightly poorer, but now they compete very well in a variety of ranges.
My use case also involves a fair amount of tripod work, and I even picked up a gimbal just recently.
So I'm glad that Sigma is making lenses which are cheaper / better for the price by leaving out OSS, because there are ways to not need it. If you figure OSS would cost another $200 per lens, which seems a little low but is in the ballpark, then with the Sigma 'trio' of 1.4 primes, the difference between the a6100 and a6600 is just about a wash.
I've always wondered what the difference is between Sigma and a brand like Canon or Nikon.
I used to have both Canon and Sigma lenses. The Sigmas felt different, and the pictures they produced had a different "look" for what was supposed to be an equivalent lens. My eye isn't trained for these sorts of things, so I was never able to quantify it.
What is it that Sigma does that makes its lenses cheaper than the others?