In the case of Widex, the feedback management is extremely conservative. This approach, among other things, allows them to achieve the desired 0.5 ms processing delay of the PureSound : it’s all about minimal processing. With losses above moderate , the aids need to do more processing and the engine can’t do it in 0.5 ms . This is why the PureSound is limited to mild to moderate loss. It also has the disadvantage of not doing much in noise (but what it does, it does it very well).
Also , the 0.5 ms delay is to reduce the comb effect , which can occur with vented or open domes (avoid that nasty robotic sound). If your domes are closed , the comb effect is not really an issue. The software blocks PureSound if your domes are closed/power .
So it is not about power but the amount of processing that needs to be done .