The mantra of never Westernising as an Eastern country is not particularly sound advice mathematically if you plan on playing to 1821.
I don't think your math supports this claim. You seem to think that math cannot leave room for opportunity cost, which is not you. You can easily account for it by considering the ROI on any and all investments you make in order to maximize your opportunities.
First of all you also missed that starting westernization drops your stab by 3 and requires you start with 0 stab, so that'll cost you about 300 more admin points.
So let's just assume you don't do that, and it costs you about 3300 points. So 55 techs with WAT to break even. Assuming those are spread out fairly evenly, that means if you only take one admin tech (won't make it much if any slower and opens the idea group) and all military techs until you can westernize, you can probably start to westernize by 1479 if your neighbor in question takes their tech as soon as they lose the ahead of time penalty. You then finish by 1494 and get started on your techs. You now have techs 4/3/8 to the highest western nations 8/8/8, so you start with a -20% admin and -25% diplo tech cost, so that saves you 630, probably closer to 700 points to catch up by the time you actually do.
So you break even when you've saved 2600 points. That occurs after 52 techs. That's about 17 tech levels. That puts you at 25/25/26. So your net gain is 10% of 20 ranks, which is 1200 points.
With no WTA, this occurs after 26 techs, which is about 9 tech levels, putting you at 17/16/17, so you save 5520 points over the course of the game.
Just like money, monarch points are worth more now than they are later. There is no way in hell that it's a good idea to spend 3300 points over 15 years to get a 36% ROI over more than 300 years. Horrible investment. If you know you're not going to have WTA for the course of the game, 3300 points over 15 to get a 167% ROI might be a good deal, but it's a matter of personal preference, and being unable to get WTA for a majority of the game is such a weird circumstance anyways that I'm not sure it's relevant.
In conclusion, my mathematical opinion is that you should never westernize as an eastern nation.