With all due respect, you are making a number of assumptions based on a very small insight of what happened in the less than a second prior to collision (rather than seeing the full video, which I have seen and which the police did see btw). Hindsight is always 20:20, especially when you can reverse-engineer a solution to the problem.
First and foremost, you mention that one of the concepts of Motorcycle Roadcraft means “taking up space and acting as if you are in a car yourself”. However, this is not the case. The fundamental concept of motorcycle roadcraft is IPSGA, the P being position and being a motorcycle you can (and should) take up different positions on the road based on the information you have available to you (the I). A car does not have the possibility to move around the road in the same way, meaning for a car the P becomes pretty much redundant. However, the P enables you to feedback into “I”. If you were to “act as if you were in a car yourself” filtering (amongst other manoeuvres) would be neither advisable nor legal.
“If you watch the second car (as the biker should've), it doesn't slow as it approaches the junction, a sure sign that it isn't going to give way but will continue into the main road.” - What is not shown in this clip (which should have been, a fault of starting the clip not showing the few fractions of a second prior) is that as car 1 pulled out of the junction, car 2 did slow and stop (away from the Give Way, but still stopped). He only started to pull out in a single movement once car 1 almost completely cleared the junction. I realise that I should have included that few fractions of a second earlier in my clip and will upload that so that this information is clearly shown. Given that car 2 was stopped albeit short of the junction, there was no reason to believe at that point that he intended to pull out.
“The biker should have been slowing for the first car” – there was sufficient time and space for the first car to pull out and clear the junction, especially given there was no traffic in the opposite lane. In a car, I don’t believe most drivers would have slowed (at least not significantly) for the first car either because there was enough space for a car to pass too.
“I'd like to think I'd have been doing 20mph or less some way before I reached the junction”. Really? You would approach every junction with cars waiting on a major A road (national speed limit) at 20 mph or less? Then you run the risk of being rear-ended by the car behind you because you are slowing down to a fraction of the speed limit unexpectedly. I have never seen a rider who slows down on passing a junction to that extreme purely on the basis of there being cars at the junction.
“As for the horn: The standard driver reaction time for a driver is 2.3 seconds” – that is the standard driver reaction time when they are not expecting something to happen. At a junction, a driver should be alert to the fact that something could happen and therefore that reaction time should be somewhat shorter.
“Having spotted that the second car had no intention of stopping” – as I said earlier, having seen the full version of the video, rather than this shortened clip. The second car did slow and stop for the junction.
“The reason the second car pulls into the wrong lane is because it's, belatedly, trying to avoid the collision...” – Actually, my belief is that the driver cut the corner in order to “beat” the car out of the junction that was approaching from the opposite direction. This would also be consistent with the fact that he slowed and stopped slightly away from the junction prior to making a single move to hurry out rather than rolling forward.
All that said, as bikers we must always spend the time evaluating both our own and others’ reactions and learning. Our constant consideration of what we do and why we make the decisions and choices we do make is what ultimately will help keep us alive. Complacency has no place in motorcycling will never have a happy ending. If this clip promotes discussion of what can happen at junctions from the perspective of both riders (none of us can ever claim to be perfect riders) and car drivers, that can only be a good thing.
However, you mention that a more experienced rider (without actually knowing the experience of the rider in the clip) would have been likely to have avoided the collision and yet research shows this not to be the case. Prof David Crundall showed that, “experienced riders chose faster speeds, often over the speed limit, especially when approaching junctions with good visibility”.
If only car drivers would give the same consideration and attention to their driving, as (the majority of) bikers give to theirs (as bikers, we do sit and analyse what happened, what went wrong, what went right, what nearly happened etc - I don't know (m)any car drivers who do the same), the roads would be an awful lot safer for all of us.