Westernization shouldn't have a reason to exist, period. I know, I know. I can feel the "Malacca! Plassey!" on the tips of your tongues. They were proof of undeniable superiority, right?
Wrong. Malacca was a specop led with superb perfection - unload on the city's main bridge, fortify it, deny access to the royal palace, shell the royal palace. It had nothing that implied technological supremacy, just a very good general with a very good plan. Of course, these things can't happen in game - that's a problem, but what can we do.
Plassey. Has anyone of you read how Plassey actually went? Because, for how it is mentioned, it almost seems like it's colonialists machinegunning the helpless natives... and French. Oh, yes, there were French as well on the Indian side. They were primitive too? Nah: the battle was against (again) a well-fortified position, and there was one tactical mistake that lead the Indian general to his death. At which point, the Indian army - a bit bloodied, but essentially all there still - retreated. Doesn't look like a rout, to me.
And someone named the Opium War. The problem being, you need some decades after the game ends for that - and while it might be a short time, it's all the time needed, because the height of the First Industrial Revolution is there.
All said, in 1820 many Asian countries (but not all of them) had deep structural problems in their societies that eventually locked them from industrialization, and led to Britain having the Maxim Gun and them not; but these things are of minimal or no impact at all, in EU4, because no system represents them.