Yeah, that's still a linear gameplay
(there's a linear path by the way and no matter how often you replay it, the story will stay the same)
Those side-missions are just to fill up "space" I think, else the game would be finished even faster. I really took my time when I played DSF, it took me 4 days to finish the story alone. I first thought games are getting easier, but we're just getting better. I always had this image that Driver 1 had so many missions and that it was so hard. Truth it, a year ago I think, I played and finished it again in less time than DSF. And San Andreas a few years ago I had finished it 100% in exactly a week (not just the missions but really everything 100%).
I do like these, however. When DSF came out I wanted to play it so bad, but I didn't want to finish the story in a day. I did free roam a lot and played challenges and stuff, but still. It made some time pass… also, I don't forget the story, plus there's the "previously in…" anyway.