You are trained in the teaching of the Messianic Voice, a group within Ex Miscellanea. You gain four forms: Gav-Riel, Mik-Hael, Ur-Iel and Rap-Hael, which governs limited areas. You can use these four in combination with any technique to simulate a hermetic order spell, as long as the intended spell does not fall outside one of the four forms' purviews.
You can also use one of the four forms in Certamen. All four together cover any facet of one of the 10 hermetic forms, eg.
Atlas of House Tytalus challenges Rebekah the Messianic Voice of Ex Miscellanea to Certamen. She chooses Rego, which Atlas accepts. He chooses Ignem, and she agrees, knowing that Gav-riel has command over light, something that falls under the purview of Ignem.
The four forms are imperfect in Certamen however, and only half their effective score is used.
The four forms are used like any Hermetic form during lab work, form bonus to Parma Magica or the likes, as long as the lab work intended or the spell defended against fall under one of the four forms' purviews.
Summae that covers a form which a Messianic form can relate to, are possible to read, but the Messianic Voice only creates half the normal Study total. Vis functions normally, as do Tractatii, if they relate to a Messianic form; if not they are unusable.
Divine Auras work at 1/3 of their level as a bonus to your magic. The other auras function normally
I would say that those would form the basics of a non hermetic tradition.
This means that with 5 techniques and 4 forms you cover the same combos as with 5 twechniques and 10 forms. Sounds like your new forms render the forms in hermetic magic useless, since putiong XP in 4 forms is more efficient than puting them in 10 forms.
It might be OK for a general tradition that is not hermetic at all, and uses 9 abilities to do the same as hermetics do with 15 arts.
It might work, but you will need to define those 4 ftorms you talk about previously
As said, I would make those into a different non-hermetic tradition, allow them to break one of the limits of hermetic magic and li9mit their abilities in an other field, so that they are still limited somewhere.