What is the right approach to research when goal is not to publish in top conferences?
I am guessing, but I think you haven't sufficiently specialized.
Most theoretical computer scientists are not specializing in something as broad as graph algorithms.  They are specializing in something extremely narrow, say specifically in list coloring algorithms, or specifically in adaptations of Lenstra's integer programming algorithm.  Your aim should be to specialize in something so narrow that you are the world expert in that very narrow area.
Don't try to understand anyone else's work completely; you only need to understand it well enough to see how it contributes to your work.  Because you have focused on your area well enough, you should be able to read (the relevant parts of) papers much faster.
The danger in doing this is that you end up producing work that no one else is interested in, but, as long as it remains legitimate research, it should be publishable in lower-tier conferences.