Having driven (and engine braked) both diesel and gas manuals - yes, a diesel is much better at slowing "very hard". Beware of doing that if someone is close or inattentive behind you.

With either one, any need-to-brake situation gets more complex - you need to decide "brake pedal, engine, or both?". But I'm not driving manuals because I want driving to be super-simple.

Interesting. I found my diesel Mercedes to not have much engine braking at all (which I attributed to the lack of a throttle plate or any throttling of airflow) as compared to similar size and weight gas cars (which have a throttle plate in the intake).

Supposedly, the engine controls in my VW diesel (90HP 4-cylinder "TDI" engine) cut off all fuel when the driver was engine breaking (no throttle, RPM's above current desired idle speed). Perhaps they made other adjustments. It could brake pretty hard that way.

I'd guess the engine controls in your Mercedes handled that situation rather differently, for "Mercedes customers will expect..." reasons.