Do not worry about things that you don't control. Our job as innovators is to find opportunities that we believe in and give our best, independent of the outcome. Moreover, Tech giants cannot focus and move as fast as a tiny startup.
And I'd like to add that there are plenty of things to worry about. Channel your energy there.
The market, and your understanding of it, should be a major factor. The fact that 800 pound gorillas have more resources is just an excuse to not do something.
Besides, those resources could just as easily be used to acquire your idea if you do it better.