You make the fundamental error made by all crank scientists. You assume that a few bits and pieces of unexplained phenomena or unknown history can be assembled into evidence for overturning mainstream science. In your particular case, you argue that the existence of a bird whose wing loading is near the theoretical limit for its type could not have existed unless gravity was weaker.
Your evidence for this is the presumed existence of predators.
You have neglected to include evidence for any wide ranging or systematic adaptations for changes in gravity over time. Dramatic changes in gravity would affect every living thing above a few grams in mass. It would affect the size an structure of plants; it would affect all birds and insects. We have excellent remains of all classes of plants, insects and birds covering the last 60 million years, and there is no evidence for adaptations for changing gravity.
You have a few bone fragments for large dinosaurs. Their reconstruction could lead in a number of directions, but you have chosen a reconstruction that leads to maximum difficulty.
But the signature assumption of a crank scientist is the assumption that major physical constants can change, or that large changes in the orbit or rotation of planets can change without catastrophic heating effects.