Hi.
You are correct in stating, that you dont't need to lean during climb. Actually a richer mixture is essential for cooling in thinner air with turbo engines. Whenever you set your cruise power setting however, leaning is still required (well recommendet at least). The same is true, if you're operating at lower altitudes below FL100. Down there the turbos wastegate would probably still be wide open and there would be little difference to a naturally aspirated engine.
The current behaviour of the Mixture levers as pure Fuel Cutoff switches seems to be wrong imo. Since they have a very long way to move, and you have EGT gauges it looks like you should be able to set them with great precision in order to get the most out of your fuel consumtion. Right now they have no effect whatsoever on either EGT or FF. I personally liked the behavior before the 1.2 update better, even if you had to lean during climb as for the sims limitations.
The POH also does a nice job explaining whats going on. Page 7-39 (71) onward.
https://hangar50.com/wp-content/uploads/2018/01/Cessna-414-Chancellor-POH.pdf
Cheers