OldnGrounded,
Certification approval is a mixture of theory, design, engineering, documentation, proof of concept, assessment, and testing. It does not depend on being inservice for some time.
There are some significant assumptions; reading between the lines, and extrapolation of what is known publicly …, … joining up the dots; but first what is a ‘dot’.
Normal stability throughout the flight envelope had to be demonstrated in certification. No abnormalities were identified (excluding the MCAS flight envelope). Indeed the Max ‘had to be the same’ as previous series.
The task is not to provide type certification without MCAS; the ‘naked’ 737 Max does not meet requirements. Within the certification process it is necessary to asses an aircraft for abnormal operation after a required system fails, e.g. 737 single engine flight is within certification, being ‘acceptable’ for emergency operation, safety recovery and landing.
The extent of 737 Max approval for abnormal operation with MCAS inhibited is not known; we assume that it would not involve significant flight restrictions - slow down, select flaps - trim. However, within that assumption, the extent and use of checklists appears to be a problem; human machine interaction.
The abnormal piloting task has to consider the overall operation with AoA disagree, other failed systems; simultaneously no MCAS - offset trim, recover attitude, continuous Stick Shake, Air Data disagree - use st by instruments, incorrect low speed awareness, increased stick force (feel diff), manual operated wheel trim.
The approval of this operation requires judgement, of piloting capability, in context, at any time, to public satisfaction via the FAA, with or without published reasoning.
First the FAA has to reacquire public trust, not change regulations.