1. No offence, you are clearly wrong - a mechanical wastegate will adjust inlet pressures, as atmospheric pressure reduces/increases.
2. it may be that an aircraft turbo system having to perform over such a large atmospheric pressure range, eg sea level to 35,000ft, the mechanical may not be able to equal the TCU
In this speculation, I would still wonder why Rotax didnt offer a cheaper mechanical option, with say a 20,000ft ceiling.
which is it skip. you appear to be contradicting yourself in your quest to prove others wrong.😁