The recent tax cuts will take a few years to filter though the economy to workers - at best. Thus it is incorrect use results to judge any policy until many years have passed. This is the nature of most things that the government does, and why it is really hard to figure out what is best.
There are ways to make judgement that are not based on results, but they always subject to their own biases.
Yes, but nobody really believes in trickle down economics. The entire name of "trickle down economics" came from people who were against supply-side economics and named it based on their (mis)understanding of the theory. Around half of economists today seem to be on the supply-side side (notably, the Chicago School and the less mainstream Austrian School).
There are ways to make judgement that are not based on results, but they always subject to their own biases.