That's surprising. From the many YouTube review videos that compare these 3 phones in camera, my impression was that honor does the most sharpening and contrast, especially for human faces. Honor ones look like the faces are superimposed, which is something I don't like. But I get where you're coming from about the plain, because honor pictures like generally brighter than the other two, making it look more pastel(?). Guess collabs with camera brands do make a difference.
Wat I feel is ah, all 3 brands (in fact I feel is all cn brands) implement some sort of face beautify mode no matter what, so when u said superimposed faces, I feel it applies to all cn brand phones to a certain extent.
For YouTubers, I have a feeling alot of them receive their phones with pre-production firmware coz they receive at least 2 weeks to 1+ months in advance, and ours being retail firmware (of course, or at least there's most probably a day 1 update to retail firmware). I can't say for sure what e firmware is based on, but my guess would be probably a mixture of more cn features with gms as base, thou it still shld be 80-90% implemented in e official global fw. This is based on what I noticed when i was able to review some OnePlus phones this year. And during oppo find x8 pro launch, I heard from ppl here in hwz is that the demo units actually produce better photos being in older/demo firmware compared to retail units shooting the same thing(hence I say the processing is the difference here)
Then for honor being the "flattest", I am of course referring to the 3 apple store photos here to compare. I cannot say for human face processing coz they are not the focus here. Framing aside, I am just looking at how the final image that's produced, and what I see is that vivo one is way more processed than the other 2, oppo in e middle and honor look the least. And honor is actually using e previous gen sensor used in x200pro, hence my saying that the processing is the difference here. It's the same observation when I compared my x200p and mi15 ultra hp9 sensor photo shooting at the same area, vivo looks more "pleasing" and more legible word, while mi15u is still blurry after multiple tries, but ppl have commented that e mi15u still looked better overall. And the processing thing also carried on to OnePlus 15 this year where theres no more "haidilao" Collab, and I noticed that op15 photos are much less contrasty and flatter compared to op13. Ppl argue is the sensor "downgrade", but I have used the said imx906 sensor phone 2x in the past before (realme gt7pro and z60ultra leading, AND it's used in magic v5 too, are the photos bad?) and can safely say it's a good sensor still, but the photos that come out from op15 is flatter hence ppl are saying it's bad..