Not really. The report says that
The safety level to be maintained in these operations is expressed as an engine failure rate being better than 1x10-5 per flight hour.
It then goes on to state that
the rate for piston-engined at 0,89x10-5 per flight hour
I.e., they are within the stated safety level to be maintained. It then goes on to say what you quote.
So, it sets a safety target, determines that piston engines satisfy that target and then goes on to ignore the target and ban them anyway. How is that proportionate?