From the article:
The available tools in Director Mode and the Rockstar Editor (and they're good, don't get me wrong) alone just don't feel robust enough to parallel the kind of options that Stunt Island offered. SI featured multiple cameras (with programmable instructions) that allowed for a single take to be stitched together to form something truly cinematic and exciting. The Rockstar Editor allows for camera moves, filters, explosions, film speed, etc. (so did SI!) but it doesn't feel as intuitive as SI, especially because creators are forced back and forth between screens to make proper edits rather than presenting a source deck and a final cut deck, but maybe that's just my rose-coloured nostalgia talking. There are some really creative videos out there created with the Rockstar Editor and I'd expect to see way more in the future, it just feels like as far as Rockstar took the options they could have taken it just a little bit further to give creators even more control.