Moved to #third-party-addon-discussion:aircraft as this is the Milviz 310R.
At higher altitudes, piston aircraft will have a harder time taking off - if you had taken off from sea-level, you’d gradually have to lean out the engine to eke out best performance the higher you go, as you’ve already done. That’s the condition you’re starting in at a higher altitude - it’s a bit of a penalty. It would be an even bigger penalty if the ambient temperature was high - the two more impactful Hs of the worst-case High, Hot, Humid takeoff.
That’s why most aircraft you see at higher elevation airfields are turboprops and turbine jets - reduced penalties for them. And the exception is Turbodiesel prop planes. TDs will hold performance all the way to the end of their envelope at max ceiling - DA62, DA40NG are two of the stock sim planes that are TDs.