For a long time, photographers with Canon full-frame cameras had to look enviously at their colleagues with Nikon or Sony cams when it came to the topic of inexpensive, fast zoom lenses. While you could find corresponding models for your Nikon or Sony cameras at Sigma and Nikon for well under 1,000 euros, there was no corresponding offer for Canon cameras...

Mechanically, the Sigma zoom is of higher quality, optically Canon is slightly ahead. To be fair, it must be mentioned that the camera's internal correction of distortion and vignetting helps a lot, especially with Canon's RF 2.8/28-70 mm IS STM. Incidentally, the classic 2.8/24-70 mm zooms from both manufacturers perform slightly better.