Isn't this essentially the approach Einstein took? He basically added a new "constructor", "the relative speed of light is the same for all observers", to exist

Isn't this essentially the approach Einstein took? He basically added a new "constructor", "the relative speed of light is the same for all observers", to existing physics models and a new more encompassing physics emerged, whose amazing predictions were born out by experiments. He didn't add that new constructor because it made intuitive sense, but because prior experiments indicated it to be reality, no matter how counterintuitive it seems.