Good point. Not all Ecoflyers are created equally.
Ours were originally equipped with the 135 HP 1.7 Thielert, and later upgraded to the 2.0 Thielert which was somehow downrated to produce 135 HP. Because the engine was downrated to produce the same thrust, used the same FADEC and the installed weight/arm was virtually the same, no new POH needed to be produced, just a new W&B schedule.
New Ecoflyers can also come equipped with the 2.0s Thielert, which produces the full 155 HP. Those versions, according to the website, have an 1100 kg MTOW and a useful load of about 460 kg, which is even better than the DR400-160.
Here is a URLs comparing the 2.0 and 2.0s side by side:
Robin Aircraft
I have never flown the 2.0s, but would love to.
Something else: If there's a requirement that the aircraft is kept outside all year round, have you also considered a DA40? The same engine issues are present but you have one further option: The Austro engine. Overall performance is the same as the Ecoflyer, although it needs a slightly longer take-off roll and has slightly worse climb performance. But the cabin is more spacious and comfortable, and they're easier to find/equip with an IFR panel. And it is better suited than the DR400 to being kept outside all year round, especially if you give it a good wax every now and then.