I just wanted to thank everyone for the great advice! I decided against Westernizing as Russia despite the button lighting up from time to time due to my poor Diplo Tech.
In my current game (mid-1600s already), I've begun regaining Russian land. The 1500s were marked with a century of shame as the Polish-Lithuanian Union + Moldavian, Trans, and Wallachian Armies marked defeat after defeat for my Russian armies. We were simply outnumbered and outgunned. When the Commonwealth finally formed, it gained a new March in Hungary. It didn't help that it also was a close ally of France. At its peak, it was fielding close to 105,000 Standing Soldiers (Commonwealth) + some 30,000 or so odd armies from its Marches. Things looking bleak and two failed & humiliating wars later, I decided to just give up on all my Western Claims and just expand eastwards. After all, even the Ottomans and Austrians were soundly defeated.
Then it happened! The Golden Era of the Commonwealth prompted it to Westernize. I observed the process unfold. Within a decade, the westernization completed and instead of a monster, a paper tiger came out! Legitimacy was way below 50, tech across the board were behind 3-4 levels each, and its stability was near gone. Needless to say, the dismantling of the once proud Commonwealth began and should be finished before the end of the 1600s. I can only imagine in horror what would've happened to me if I clicked that Westernize Button. It's clearly a trap!
