The term Holy Trinity dates back to the 70's, according to WatchBox
https://www.thewatchbox.com/blog/holy-trinity-watches.html#:~:text=the%20Overseas%20collection.-,What%20Brands%20Make%20Up%20The%20Holy%20Trinity%20of%20Watches%3F,Patek%20Philippe%2C%20and%20Vacheron%20Constantin.
This is long time before a lot of modern independent watch makers who make even more complicated, more sophisticated, more innovative watches than AP/PP/VC. Just 3 places are not going to fit these brands.
And if you want heritage alongside high-horology, we're also living in a special era of watch making, where a lot of 100+ YO brands are revived, rejuvenated financially and hence making some ultra-complicated watches with an 18xx, 17xx name on it. Still you probably need 10+ places to fit them all.
So we can debate about the new top N watchmakers, but to me AP/PP/VC deserve to stay as Holy Trinity, for the fact that they were doing an excellent job back in the 70's, the last era of pure mechanical watchmaking before Quartz Crisis, before all those M&A by investors and big groups, before marketing over watchmaking, and certainly before the influence of hype and flex culture we have today.
In the name of Audemars Piguet, Patek Philippe, and Vacheron Constantin,Amen.