This isn't true when wearing a helmet alters behaviour of the user or other road users. In the UK it has been found that motorists leave less space for cyclists who are wearing a helmet, and that helmets increase risk-taking behaviour.
It was one study on car driver behaviour. It was on roads I use.
Most experiments on helmet use shows increase in risk behaviour of the wearer. Observational studies are less important for decision making.
Doesn't your car have seatbelts and airbags?
2 meter drops that achieve about 14 miles per hour (22.5 kph) on the flat anvil. In Europe the drop height is only 1.5 meters. Why so low, when bicyclists frequently exceed 14 mph in forward speed?
The typical road or trail bike crash involves a drop to pavement. The important energy in that crash is supplied by gravity, not by forward speed. Although forward speed can contribute some additional energy, the main force is the attraction of gravity, and the impact severity is determined by the height of your head above the pavement when the fall begins. It is gravity that determines how fast your helmet closes with the pavement. Some of the crash energy is often "scrubbed off" by hitting first with other body parts. The typical bicycle crash impact occurs at a force level equating to about 1 meter (3 feet) of drop, or a falling speed of 10 MPH. The rider's forward speed before the crash may be considerably higher than that, but the speed of the head closing with the ground, plus a component of the forward speed, less any energy "scrubbed off" in other ways, normally average out at about 10 MPH.
So bike helmets are tested with a 2 meter (6.56 feet) drop. Motorcycle helmets are tested at 3 meters, about 17 mph. A really good bicycle helmet can handle
https://helmets.org/limits.htm
The (now foolishly down-voted) comment that you are replying to is exactly right that a bicycle helmet would mitigate the shower scenario injuries.
That doesn't mean the technology can't be improved, and there's actual science being done. Brains are being imaged. There are peer reviewed articles published every year that details the challenges of how to model brain damages. It's not fair to brush them off as just an invention in marketing.
So far it does seem that measuring impacts at an angle matches real world brain damages better than the older standards of measuring dead-on impacts. That's what "rotational acceleration" means. Acceleration is just another word for impact. It doesn't mean your skull should rotate freely.
There are enough indications that this translates to helmet improvements that most consumer organizations have started to recommend them should you buy a new one. That doesn't mean you should throw away your old helmet but it should be enough to disqualify it as "snake oil".
This new Wavecel system hasn't been reproduced yet, two testing institutes has so far failed, but it is similar enough to existing cell and slip systems that performance is not likely to be worse.