The recent downing of a russian A-50 and other EW aircraft suggests UA is targeting Russia where it is the weakest in order to “blind” russian forces and prevent them from using their most advanced weapons efficiently.

There's no such thing as a game changer weapon, however, beyond the impact of western weapons’ superiority, perhaps an answer to your question would be the superiority of UA and its allies in both the targeting cycle (see OODA loop) and overall ISR capabilities.