I think "MIND THE GAP!" (when a recorded male voice pretty much shouts it[1]) on the platforms with the sharp curves and wide gaps is fine — it's unusual, and especially useful for visually impaired people.
The more common "Mind the gap" with the female voice is worse than useless, as it is used far too often, when there is barely any gap, and detracts from the significance of the other announcement.
"Hold the handrail" is ridiculous; we should expect some personal responsibility from people. I laughed the first time I heard this, 15 years ago in China, and was disappointed some years later when I first heard it in Britain.
It would be interesting to see statistics on accidents before and after these messages were introduced.
Any time there is "helpful" commentary like that, whether in a tube station or in software, it tries to make individual consumers responsible for what is in fact a design flaw.
I'd hesitate to call it a "design flaw" though, bearing in mind the design for these stations was from the 1880s-1910s. There were much different requirements then: far fewer passengers were expected, all of them able-bodied and most of them locals. It's clearly a compromise, as it allowed the station to be where it was wanted rather than on a straighter section of track.
I don't know what alternative there is to escalators — lots and lots of lifts?
Either it's the nanny-state gone mad (with people trying to justify their jobs), or it's the lawyers who advised that "that way they can't sue us". Either is plausible in 21st century London.
In any case, they can be over the top and really annoying. In some stations they have presence detectors at the bottom and top of each flight of stairs so that as soon as someone passes through they are told to "hold the handrail and take care"... Which means that when walking from entrance to platform you may be told 4 times to "hold the handrail and take care".
At this point I just want to rip out the handrail and destroy the loudspeakers in a rage... But I am conflicted because TfL also keeps telling me that I should be kind [1], patient [2], and considerate to others [3], plus someone might report me [4]
Perhaps there is a reason Black Mirror is British.
[1] https://images.app.goo.gl/kKDe7E2GzKFdefVa8
[2] https://images.app.goo.gl/octoWDN7uYuPSMTz5
[3] https://images.app.goo.gl/sX7rYKRxVk8Kq9Be8
[4] https://images.app.goo.gl/y4uDdmjruySP22mb8