If an original (used) battery is installed, it should be recognized as original and graded accordingly to its state (let's say 80% of what it should be).
The current provision doesn't prevent the use of a defective or used or sub-standard battery, it only prevents non-Apple personnel from performing a repair without triggering the (possibly unjustified) alarm.
This is a pro-consumer move, because it gives the consumer more information about the state of a product. They can ignore it if they want, it doesn’t impact the operation of the device.
This is not pro-consumer any more than saying that only Ford-certified auto shops are able to disable the "check engine" light, because Ford can't guarantee the performance of auto parts they can't certify are genuine.
There’s also the possibility of repairs being performed with used or otherwise tampered with genuine parts, which are almost as much of a wildcard as third party parts.
Maybe things have improved with smartphones, but I remember third party replacements for MacBooks with swappable batteries being worse than a crapshoot — on top of bad capacity and faster degradation they also often caused kernel panics and power management issues. I can see why Apple might want to not be stuck with supporting that.