I'll admit to being a Rotax and Tecnam convert - and not just through work (we maintain over 40 various GA aircraft - Rotax, Lyc and TCM powered) - my own aircraft is powered by a 912S, my previous a Lycoming.
I can see your point about 75kg persons but please note I didn't say '3 adults', I specified the weight which gives a better real world figure for people to compare too. Quoted cruise speed is similarly real world IAS not 8000ft TAS...
I'm sure there are different reasons why Cessna binned the Rotax in favour of the O-200D - just depends who you speak to...!!