The ability to predict the trajectory of an object comes from Newtonian physics. You analogy is similar to, if i'm good in Chemistry, then i should be good in aerospace mechanics too?
And being a researcher, most of my experimental work is preceded by hours of theoretical work and simulation, We do not predict, we analyse the data, and change the parameters to yield desired outcome, and replicate it in experimental processes. And since last decade, the big bang theory didn't had any experimental data to back up it's claim, but a lot has been done in the past decade to prove it.
And your 'claim' is not a theory. A theory is an observation, and recorded as a repeatable and quantifiable data.