How often are people getting a throttle jamming open? Just curious seems like a fault with the throttle and would be a rare occurrence and at that point couldn't you just switch off the ebike. My on/off switch is on the same part as the throttle itself. Seems far more likely you need brake sensors to me with a cadence sensor as the one's I have tried have more lag so there is a delay in stopping pedalling and the motor not powering and you can accelerate the motor stopping by applying a brake lever. If you didn't want to wire up brake sensors you could fit a simple motor cut-off switch somewhere on the handlebars that uses the same brake circuit just in case of emergencies.
Its very easy when you have a full width throttle because you're holding yourself with it , and when you hit a big bump, you can rip it past the stop, then you get permanent 50% throttle.
Thumb throttles can do the same if you drop the bike and the lever catches on something, but it's almost impossible to break one while riding. All other problems apart from water ingress tend to be there before you start the bike, in which case the controller won't give power. That leaves water as the main danger, but I never had anything like that in more than 10 years of riding in all weathers. Maybe it could happen if you leave your bike leaning over in the rain.
I've never used brake sensors in the last ten years. The only time I miss them is when I have to do a very sharp turm back on myself to go from the cycle path up a parallel path to a footbridge over the road. You can't pedal while making the turn because the motor throws you off balance. You need it on maximum power to go up the path to the bridge, which is about 15% and you're approaching up a steep hill already, otherwise I'd have it on level 1 and hit the throttle as soon as I turned.
if you have that lag on your controller when you stop pedalling, get rid of it and get a decent one. Those ones with lag are normally pretty terrible all round, but if you must stick with it, then you need brake sensors.