There'll never be another rapids ride built in the UK, and I honestly believe that within the next five or so years those that still exist will have been closed - the guidance is just too restrictive. But, quite possibly, this is what the HSE wanted all along...
You might be proven wrong seeing as Paultons is currently building a water ride heavily rumoured to be a Hafema rapids ride for 2024.
With that being said, I agree with your overall point. The HSE guidance all but forbids parks from employing effects that encourage people to stand up, which rules out any of the old classics like waterfalls, water cannons and such, as well as overly forceful wave machines.
If you think about it, it is almost a wonder that the HSE allowed rapids rides to operate as they did for so long. I’m not saying that rapids rides are/were unsafe by any means, but there is a lot of risk involved in operating them compared to other ride types.
Things like roller coasters with no restraints and block systems died out decades ago; modern roller coasters have restraints, block systems, upstop wheels, and all kinds of other failsafe mechanisms to make them completely foolproof.
Rapids rides, on the other hand, have no restraints and no way of controlling the boat’s flow past the station other than through the use of very blunt instruments like those roller-type things that you see every now and then on Congo. They are arguably not failsafe in the same way as something like a roller coaster, or even other types of modern water ride, because you have little way of controlling a boat that is freely flowing down a river and the guests seated within. Some responsibility for staying safe is handed to the guest, which is always risky, and there are no ways to control the flow of boats past the station. In the same sense as block sections, at least.