I guess you misspelled Cancellara where you wrote Sagan?Of course Sagan is a legend of the sport, are you guys freaking kidding me? By far the best and most consistent rider in the world from 2011 to 2017,...
There are some riders, in the last 10 or 20 years, that the competition was genuinely afraid of. Cancellara ofcourse, but Sagan as well, especially in his prime (e.g. Flanders 2016), and Froome (virtually every first uphill finish in the Tour). Gilbert (the 2011 version) would qualify as well. But that's about it.
Modern-day riders that have the same pedigree are VdPoel and Evenepoel. If those guys attack, the competition knows they have to get on the wheel ASAP or they will just keep riding and crush everybody in their wake. WvA seems a bit less dominant but he is very mature in his tactics, and his skill set is extremely well-rounded. So he can either try to go for a solo attack (Strade), try to follow the best guy in the race and finish it in the sprint (MSR) and probably finish it off as well in smaller groups (up until some bigger pelotons after a harder race).