I think there are two problems one countries even non western ones are too far ahead in tech. This sometimes means that even non western countries are high tech. Westernisation is a little bit too easy maybe increase the costs or increase the tech behind that is required? I would suggest that at the end of the game most countries should stay un westernised and should generally be a little more behind in tech.
What? Men, ROTW small and medium sized countries are lagging in tech significantly. Ming super tech issue (if they are alive) is a consequence of "bigger is always better" game design philosophy. +3 advisors and not much MP sink holes for big country (no WE, all revolts are manageable if existent, Ming have rather peaceful AI any other way they would wreck every one and their mother before Europeans arrival) are good mix for good tech.
Ming was slow bureaucratic machine, which was kicked by peasant revolt a while ago, but ridiculously low taxes stay for a longer while (you know, populists are tops in breaking countries quickly and efficiently). Any way who would want to pay high takes, fight in wars with some "backward foreigners" if you could stay as you were, not risk any experiment (failures are inevitable), don't have obligation to fight somewhere and pay high taxes at the top of that?
I would like to see some event/decision to decrease/increase tech cost (reform administration, government/diplomacy/navy or military) at expense of higher build and maintenance cost and build time for army/navy (CA, morale nerf?), stab and coring cost, revolt, tax/trade/production efficiency (it's all about collecting taxes during rapid changes). Until monarch's death with some chance to prolong effects if heir is good enough. That would eliminate need to westernise at least in some cases. Perhaps make westernisation easier giving, but give non western neighbours CB "Pacify militaristic neighbour" (prestige, perhaps chance to get some invention by themselves) or uprising if next monarchs are not good enough (+tech cost +unrest as demands or lower tech group if they manage to enforce).