It can become boring when one team is very dominant, as has been the case for a number of years now. Absent that though, differences between the cars can make the sport more interesting. The engineering competition is a part of it. As are the adaptations the drivers and teams need to make to take into account their cars' relative strengths and weaknesses compared to others. Plus, if the disadvantage isn't too great, it can be fun to cheer for an underdog who overcomes a disadvantageous car and still manages to win.

Spec racing certainly has its place, and it is indeed also nice to see drivers pitted against each other on skill (and luck) alone. But that's never been Formula 1.