Western can afford a string of mediocre rulers a heck of a lot better and in the late game has vastly superior units. Also, the western nations listed have significantly stronger military NIs than Russia on top of the superior units.
You do realize that the very fact that Western and Eastern are comparable to eachother should tell you to how strong Eastern is. Eastern has 20% penalty which is reduced to 10% with Russian NIs. 10% is nothing as far as tech group penalties go. Ottomans have 25%, Muslims have 45% penalty, Indians have 50% penalty, Chinese have 60% penalty. On top of that, Indian and Chinese only have base MP growth of 2. I wont even get into the New World/SubSaharan/Steppe. Then you have Eastern mass infantry with 52 pips. By comparison, Napoleonic Square has 60 pips and everyone else has 38 pips (Ottomans) and below. The Chinese lategame infantry has only 28 pips. For all intents and purposes Eastern tech group can curbstomp asians just as well as western can.
Eastern is the only tech group that can get away with -not- westernizing, and not westernizing is a good idea because how much of an MP sink westernizing is. You have to fall 8 techs behind, you lose all your MP and get -100 in the hole, and on top of that you get tons of events during westernization that removes monarch points.
As for Russia having terrible NIs?
What are you smoking, and can I have some?
+50% Land Forcelimits
+125% Manpower
+10% Manpower Recovery
-10% Tech cost
-15% Core cost
+0.5 Army Tradition
-50% Infantry Cost
+10% Production Efficiency
Its pretty much a consensus that Russia has one of the strongest NI sets in the game. Prussian ideas are the only ones that are definatly stronger, most other European countries only get +10% Discipline which is not enough to offset the LFL and Manpower advantage. Sure Sweden also gets rediculous modifiers but thats entirely because of the event modifiers, Sweden actually has a fairly mediocre NI set if you take away the overpowered event mods.
Against the ai, the 3 nations listed have laughably easy times dealing with the so-called threat of "each other"-England can simply abandon the continent, France can just overpower Spain and England, Spain can make nice with France, eat Portugal, and colonise the rest of the world and Austria/HRE is no immediate threat... On the other hand, an early game Muscovy has the potential to be wrecked if the neighbors decide to go after it instead of each other as they aren't noticeably stronger than their neighbors, particularly when lacking the lucky nation bonus.
If this was true, then why is it that we regularly see a giant green blob in Siberia and China while France, England, Spain, Portugal, and Austria end up at their historical sizes, barring one of those countries getting lucky with a PU?