You just have to realise that not everyone can be on 24/7. To play some of this shit requires hours of warmup and to shoot a video spot you might only get an hour or so, so it can be unfair to nitpick shit like this. The hardest thing rusty does is the 4nps stuff with the stretches between the middle and ring finger. Harry, the speed will come with time, I'm sure if you want to achieve it in the first place, and are dedicated you could do it. But that being said, if you have no need for speed, then your time would be better spent practicing different stuff.
I'm by no means a fantastic amazing guitar player but I attempted to ape rusty on a track the slice the cake bass player did. Improvised, one take, on my first time playing a seven string.
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Tracks called how to crash a Boeing 747