It is interesting to analyze the dromaeosaurids and the troodontids.
Let's begin with the dromaeosaurids.
The dromaeosuarids fall into two groups. One group includes deinonychus, microraptor, graciliraptor and utahraptor etc. This group dates to around 125 mya. If we look at the characteristics of this group we find flying bird characteristics such as aerodynamic flight (asymmetric) feathers.
The other group of dromaeosuarids includes dromaeosaurus, saurornitholestes, bambiraptor, mahakala, unenlagia and velociraptor etc. This group dates to around 75 mya. In this second group we find flightless bird characteristics, such as only symmetric feathers.
And we find troodon and saurornithoides etc from around 75 mya with flightless bird characteristics.
The fossil record (even if incomplete) tells a clear story. Flying birds were from very early on, with flightless birds later (closer to today).