Is the Roman senate the most powerful part of the Roman government?

yes the senate is, to an extent. The actual, most powerful part of the Roman government was the Roman people (during the republic) The senate was a consulting body only. They could not actually pass a law. Laws were passed by the voting assemblies made up of the Roman people. The people also had tribunes who had the power to veto anything the senate proposed. But the senators were clever and could and did pass resolutions which had a similar effect as a law if a tribune didn't veto them. Of course all this political posturing faded away during the principate when the emperor held the supreme power.