The legal definition of recklessness requires that the person know (or should know) that the ride is dangerous. Legally, it is more difficult to prove when that person took actions that suggest they did not think it was dangerous.
To your point about broken safety features:
One could potentially even argue that the brake isn't a safety feature. It could be there to help riders that are scared of going too fast to more easily control their speed, simply for their own enjoyment. I don't think that use of the brake would be required under normal operations and therefore, it could be argued that the brake wasn't a safety feature. I personally don't think it makes sense that a "safety" feature is optional and relies on the rider, but I could be wrong. The designers were certainly negligent in other ways....
Not sure if that follows or if it makes any more sense to you, but legally, its a potential argument.
[0] https://www.wycocourtks.org/uploads/4/4/1/2/4412070/2018-03-...
While in general safety features can require a competent user, e.g. the brakes in your car, in the case of amusement park rides that allow children that does indeed not make sense.
But... I would argue that this is just evidence of substandard design of the speed control system. There is ample evidence of a history of injuries due to excessive speed.
(IANAL, though. Legal definitions of those words may not match my intuitive understanding of them...)