Also makes it harder to apply the throttle out of corners
I watched that video of Lando Norris in Austria and he is clearly told to "hold it" for a few seconds. It's current implementation of on/off toggle, certainly doesn't fit with this. It just makes it a faff to use. The most effective way to use it as a brief burst for a few seconds coming at the start of a straight to get you up to v-max quicker, having it as a hold is just much simpler way to use it. In real life they wont be using it through corners or in traction zones.
Maybe the on/off toggle is easier for controller users ( i use a wheeel) but there should definately be the option at least