The propulsion efficiency has much more direct effect than pylon drag.
In fact, for Takeoff and climb performance, the overall glider drag has secondary effect compared to aircraft weight and available thrust.
Without fuselage interference and opportunities for larger props, the pylon mounted motor provides a significant efficiency advantage. This has a direct effect on climb performance in terms of climb rate and altitude gain.
Running large battery packs, beside running cooler, also provides better energy efficiency and installing large batteries in the wing reduces overall structure weight and provides better flying handling characteristics due to CG.

FES is a nice solution, especially for retrofit of existing gliders.
For a brand new design, there are opportunities for better optimizations.
Is GP at the optimum, probably not (yet:-), but they have certainly made good design decisions for both teh glider and the propulsion.