Let's get back to https://forum.atlas-games.com/t/on-the-religion-of-magi/9989/1:
to https://forum.atlas-games.com/t/on-the-religion-of-magi/9989/1:
and to https://forum.atlas-games.com/t/the-break-room/102/1:
That is more than "suggesting".
I am with you here. Mythic Europe holds many religions and faiths, which magi can adhere to. Only very specific magic traditions - like HoH:MC p.33ff The Huntress of the Woods, or TMRE p.124ff The Children of Hermes - require a specific faith from their followers as a matter of course.
People following Hermeticism, more structured philosophies like neoplatonism, or the budding aristotelianism of 13th century medieval academy, take an intellectual approach to faith, and thereby are very unlikely to follow any religion blindly.
For a Church father with such an intellectual approach look at Augustine (see en.wikipedia.org/wiki/Augustine_of_Hippo), who also in Mythic Europe inspires many medieval scholars.
Already the Gift and the existence of dozens of powerful individuals practicing magic are artificial features introducing 20th century fantasy concepts into the game world of ArM5.

A magical society with no common philosophical belief structure, no real or imagined occult insights, and no relationship between their magic and their religious belief feels not only anachronistic but artificial. In a time when mundane craft guilds professed mystical secrets, an Order which rejects such secrets and casts world altering magics based on completely empirical principles feels badly out of place.
The ArM5 Order of Hermes attempted to gather all the powerful, Gifted practitioners of magic in 8th century Mythic Europe - within the geographical limits of its reach. The purpose was to make a lasting peace among them, and to regulate all remaining violence. Religions or philosophies explicitly did not play any role in this: even Guorna the Fetid was invited. So the Order started as a very mixed bunch, and at uneasy peace.
Even the idea of a lasting peace among individuals disparate to such a degree, and not sharing a common religion, is completely anachronistic: the typical 13th century man would consider it a miracle, or a deceit of the tempter.
Magic Theory, however, is not just empirical: the roles of experience and reason in magic are contended between The Collegium and The Lyceum (see A&A p.10). As Hermetic magi have learned magic as apprentices of others, many who do not follow such discussions will practice magic as a highly complex art.
In Mythic Europe, those testing the limits of natural philosophy adopt the classical term empirici for themselves (see A&A p.67). You should carefully verify the time, when "mundane craft guilds" who "professed mystical secrets" appeared.

Exploring the ideology and philosophy of Magi fits the pattern of gradually deepening the detail and richness of Mythic Europe. You certainly may disagree but I do not see any particular conflicts with the published history or structure of the Order.
There can be many magi honestly believing that the Order of Hermes needs a common faith. In some campaigns they may even succeeed in proselytizing it.
But I see more magi with an intellectual approach to their own religion, who use classical and medieval philosophy to find and understand their role in the universe. And to such magi also Hermeticism can be useful.
Cheers