I don’t think there are any rules against making things easier if there are corresponding increases in safety and awareness. I
Agreed, systems such as TCAS come under this description.
However, pilots do need to understand and monitor their flight systems and modes. Dumbing down flight displays and not requiring a reasonable level of ability will lead us to a bad place - children of the magenta and all that.
If the FMA had not yet been invented, then this proposal might be worth considering, but it has, so the information is already there. I am comparing this to the Airbus PFD and FMA which seem to give all the information required in a very clear manner. Perhaps the Boeing version is more complicated and/or less understandable? I don't know.