I think the hot Dubai weather has gone to your head. The Phenom out performs published figures. Manufacturers can not publish inflated or incorrect figures. The legal department will see to that. What a lot of twaddle.
Most VLJs have engines flat rated around 25 C, meaning their performances deteriorate exponentially above these temperatures (takeoff dist & climb). I'm not telling you manufacturers are cheating, they just forget to show you their limit. The Dubai air is 80% of the year warmer than these VLJ flat rating limits, meaning they will almost never be able to perform as per their advertised performances. On the other hand the Avanti's flat rating is at 52C...
If somebody wanted to operated a Mustang at its operational limit of 44C (meaning the aircraft would stay on ground if warmer) the takeoff distance would increase by 70% while the Avanti would still be 8 degrees below its flat rating limit.
I'm still waiting for you to explain me what is the added value of the VLJ which would compensate these performance losses? How do you think a Mustang would fly on an engine out climb at MTOW & 40C?
It wouldn't have been difficult for Piaggio to use 2 Williams or PW jet engines instead of the PT6, but this wouldn't make any operational sense as the aircraft wouldn't benefit from increased speed or lower noise while it would burn more fuel and loose performances.
At the end of the day we are talking business, and the 21% increase in turboprop operations speaks for itself while all other categories are dropping. Isn't it a more reliable figure than individual "perception"?