Why not motor clips as opposed to retainers?

[bad_idea]

Z clips, Kaplow clips, or any other clips are garbage for HPR Rocketry. A several gram ejection charge will bend clips the wrong way and you will lose your motor - guaranteed. Positive motor retention like aeropack or slimline are must haves for high power Rocketry- certainly level 2 and higher motors (J impulse and above). I have RSO'ed and witnessed enough flights to know fully what works and what doesn't.

For motor ejection or for electronic ejection with rockets that don't isolate one section of the rocket from another, I agree with your concern.

A mitigation is to seal the motor off from the drogue bay and to fly solely with electronic ejection, which I feel is more reliable anyway, not that I'm a clip fan (or user). At that point retention is a minor concern.

Edit for rewording.