Basically, if you think of the Sigma 24-35 as a zoom, it completely falls flat on its face due to the short range. Why wouldnt you have a 24-70?
Well, if you reframe the context, thats when it shines. If you think about it as a decently fast 24, 28, and 35 prime in a single body, thats when it starts to make sense.
And its dazzlingly sharp compared to basically every 24 to whatever zoom I've ever used. Not sure if the nature of the optical formulas necessary for the 24-70 range that make them so unimpressive, but every copy of Nikon and Canon 24-70 zooms Ive ever used have been sorely disappointing in sharpness and contrast compared to the primes I use most often.
I sold mine (stills version) because it didnt fit with my workflow and needs at the time, but especially for multicam jobs it seems to be a great candidate for a B cam imho. It for sure takes some mental bandwidth to get used to shooting within its strengths and understanding its limitations compared to the traditional zoom vs prime paradigm though.