I think the complexity of modern aircraft has resulted in a situation where pilots no longer have a complete understanding of all the interactions between the various components. Even the manufacturers get the design wrong or make assumptions about how the aircraft will be flown.
The twin supply tanks were designed to give four minutes extra duration when the smaller tank ran dry, allowing a single engine landing. No account was taken of the direction that a helicopter might be flying an orbit and that the tanks might not drain symmetrically.
Modern appliances in general have become so complex that we have no choice but to follow the manufacturers advice as to how to get best use from them. That applies to aircraft, cars, computers, domestic appliances and all manner of other gadgets.
Older pilots will be highly suspicious of relying so much on technology, young pilots just go with the flow and accept all the help automation offers. I would suggest that the cross over pilots who learned to fly using manual methods and who were then effectively forced to adapt to automation are those most at risk of having an accident due to not following the manufacturers guidelines.
They have sufficient experience to know when a cockpit indication might be spurious and have previously demonstrated the ability to fly without all the automated assistance. So they are more likely to be complacent in their ability to handle things if and when they go wrong. But the complexity of modern aircraft means that the pilot's complacency is plain wrong and not everything works how it should given their previous knowledge and experience.
The roll out of advanced safety equipment in cars hasn't significantly reduced the overall accident rate, but it has done a great deal to mitigate the consequences of a collision. Older drivers frequently mistrust and are confused by all the options available, but the younger computer generation just accept that is how cars are. Every weekend used to be occupied with car maintenance of some sort but now the car gets taken to the garage once a year for a service and MoT and no one has any idea how it all works. How did VW get away with their emissions fiddling for so long?
The design of the EC135 fuel system is typical of the current practice of introducing too much complexity. If you want to get every last drop of fuel out of a tank, use a flexible hose with a big brass nut on the end to weigh it down. It draws fuel from the lowest point of the tank no matter what the orientation of the aircraft. Make switches in different shapes and colours for different functions. The most aesthetically pleasing visual designs are often the least functional to ise in an emergency situation.
The AAIB report also makes clear that the manufacturer assumes that the radio altimeter and landing light will be available for autorotation, except you need to turn and operate the shed bus switch to activate them when both generators fail. Virtually impossible!
Another big gotcha is the rotor overspeed alarm sounding in an autorotative state. So what if the rotor rpm exceeds 106%? The more rotor rpm the better, so long as it doesn't fly apart. It isn't like you are going to be flying away any time soon after a dual engine failure and autorotation to the ground.
There have been a great many failings all around from the designers through to the writers of the operators manual, all indicative that no one person understood all the aspects of the design. But the bottom line is that it is the pilot who carries the blame when it all goes tragically wrong.
Stereotyping and over simplification is just my lazy way of avoiding typing several pages of post. It doesn't mean I haven't read the text books or lack understanding of human factors, design or engineering. I have worked part time as a diagnostic engineer over many years and investigated numerous accidents, but only took part in one aviation one.