The Americans might have a thing or two to say about it...
But even otherwise, I disagree. Every nation has their individual history. Look at Japan and how much we know about the Shogun Era, or the honorific suffixes they use.
Even Chinese history is now coming to new light with the Qin Dynasty and the three kingdom war or atleast you know Sun Tzu.
What I'm getting at here is that native authors seem to hesitate using references from their culture and fall back on western culture because it's more readily available.
All the best for your story.
It might be the case with schools across the world teaching Shakespeare while not bothering with any native authors...
But there have been several countries that have done exceedingly well in using their soft power to promote their nations as well. Just look at S.Korea and Japan. Manga, LNs and webfics from those two countries are popular around the world.
It also helps that a lot of stories on SH are generic medieval isekai fantasy, and that means Western.
Isekai doesn't need to be Western even if it is set in a medieval fantasy. Isekai is just transportation to a new world iirc.
It's easier to write western medieval sure. But I would really like to read a Zimbabwean Isekai. Maybe it can be about fighting colonization even.
You can write in English. The setting can be in PH.
If we can know kun, chan, sama and san, along with which rank higher and lower. Sure we can memorize a few PH honorifics.
Also, Chat Rules mandate using English. Let us not summon the great Tony.