The TU Delft findings should not have been a surprise to anyone who looks at the control architecture of the Airbus that was evaluated. It has a PI control loop running C*. so that is pretty straight forward, and indicates that the aircraft has no speed stability in the normal control. Boeing uses a C*U program, where the "U" is the speed stability component. The Boeing driver sets the reference speed with the trim switches, analogous to a conventional aircraft in outcome, the plane will pitch to the trimmed speed (AoA). As the Airbus is neutrally stable at all times (it doesn't really care about speed as a control target, it is driving a path determined by g or pitch rate... it goes where you ask it to) the only feedback that is needed is a suggestion to the pilot as to the fact that he has a force above breakout applied to the SSC. Airbus also provides envelope protection cues in low speed/high AOA cases, for longitudinal, and with an over bank case for roll channels.
Feedback for being "off speed" is inconsistent with the g/pitch rate of the C* system. The asynchronous controllers however leave the other pilot out of the loop as to what inputs are being made, other than on the ground where the ADI cues are used. Gulfstream has crossed the streams by applying synchronous controllers, with haptic feedback. I fly a much older G that is fly by cable, so am not aware what control logic was used, but haptic input by G would only make operational sense in normal flight for a C*U type system using SSC's, or by the C* logic of Airbus for envelope protection.
Personal experience on the 320/330/340-300 and 600 vs more experience on the B777 and 787 makes me appreciate the Airbus system in normal flight conditions. In wind shear, crosswinds, turbulence or with control degradation, Boeing is more comfortable to my tastes. The Boeing C*U has a higher tracking demand for the pilot, but there is feel for the dynamic response of the aircraft, whereas with the Airbus, intervention in perturbations to the flight path can lead towards APC problems (PIO's by another name). Both design architectures can give wild rides when they go weird from sensor failures or any other anomaly that goes outside of the expected failure modes, the 772ER/RR ex Perth was nearly as unpleasant as Kev S's A330 oddity with QF072. Both made a mess of the interior, heads, etc and gave the crews interesting problems to deal with.
Aside from the active SSC on the G500/600's the Dassault FBW offers a slight variant to the Airbus system, which is system behaviour feedback such as vibrations, as cues.