Myath could benefit from Coincounter's treatment

[Rongway]

Not every stack mechanic needs to be marked with an explicit stack mechanic marker when the mechanic is actually "discern between these two mechanics".

The Myath fight in particular features two opposite mechanics that you're expected to figure out based on color of the slimes. Figuring out the difference between red and blue is enough. And it even meets accessibility guidelines by using additional non-color indicators! The mobs are named Blood vs Rheum, and the marker shapes are distinct from each other.

Yes, we definitely have an interest in consistency, so fights that feature stack mechanics as their own mechanics should have stacks marked. But when two mechanics are happening simultaneously or in rapid alternation, I think it's fine not to mark the stack part as an explicit stack and let the players discern the two mechanical components from each other. For comparison, it would be little different from pairing or alternating a PBAoE with a donut, and not explicitly marking them for the majority (or entirety) of the castbar--for example during Qitiang Dasheng's split, when they simultaneously use Both Ends, you're expected to identify the one with an oversized staff as the donut and run to him.

The game in general seems to agree with you, however, and has been pretty generous even with these types of mechanics--for example, Alexander Prime's orange and green, or Omega M/F's orange and pink; both explicitly mark the stack part of their respective mechanical complexes.