When Formula 750 grew into a full open 750cc World Championship series, no less a rider than Kenny Roberts cast doubts upon the safety of racing at speeds of over 200MPH, with a throttle which I think he was the first to describe as an on/off switch.
Apart from the narrow tyres mentioned, they were also still treaded, slicks had yet to make an appearance, and they used to race these things in the wet.

Kenny was all in favour at the time of introducing a maximum 350cc capacity limit.
Meanwhile, being a skilled engineer Kenny was experimenting with fitting heavier crankshafts into his bikes to make the power delivery more controllable.