A very cogent suggestion.
Early on, there's a high level of symmetry partly because the mechanical complexity hasn't been sufficiently introduced yet to compensate for deficits in capability of "fundamental" tools, i.e. critique and shields/reflectors-- or, simply put, to make the new player experience somewhat deck-composition-agnostic. This may become less the case as the player progresses and certain distinguishing characteristics between the modes become more apparent.
Currently, there are some generalities of distinction for each of the modes which, depending on player progress, may not yet be obvious:
- Most negative status cards (e.g. Slow Burn, +Damage) require Ethos (either wholly or as a component).
- Logos has a wider variety of critique cards-- it's the only mode that has criticisms which "specialize" in all three modes (Contradiction -> Logos, False Authority -> Ethos, Misleading Affect -> Pathos).
- Pathos is the only mode that can pitch the Enthymeme toward any of the three modes, and it's also (subtly) the easiest to summon a lot of premises for (due to cards like Epizeuxis and the converter cards).
... In addition to the subtler variance in capabilities provided by "unique" rhetoric cards (e.g. Ipse Dixit, which wipes out fresh premises) and resonance effects (e.g. Probatio Diabolica, which zeroes-out all fielded premises, ignoring shields and reflectors).
Still, I'm sympathetic to the idea that these differences could stand to be exaggerated.
Here's one possible approach: Shields and critiques progress in stages (I -> II -> III), with higher-stages having stronger effects (1, 3, and 5 HP for shields, or 2, 4, and 6 damage for criticism). To make the three modes more distinct, it's possible that the third stage of this progression could only be obtainable for one of the three modes-- let's say that only Pathos gets Level III shields, and only Logos gets Level III critiques. This would effectively turn Logos into a criticism specialist, and Pathos into a defense specialist-- the other modes can still do these things to a certain extent, but to get the best tools in these categories would require changing your deck's color composition.
Is that a particularly good way of going about this? I don't know yet-- I came up with this idea in like 15 minutes, after all-- but, subjective quality aside, it's definitely a solution!