All this pre-occupation with the driver, yet it was the presence of trees and their leaves that caused all of this. A tree can't fall across the line if it isn't there, which it shouldn't have been. Likewise, the leaves, mostly from the forest above the junction, which shouldn't be there either. Oddly, other tunnel locations have been cleared of trees in recent years, although I don't know if it has been maintained. Whiteball, Dainton and Honiton, on this very route.
I suspect that most would (and given the account of discussion about vegetation clearance and the costs) recognise that this is a (if not the) major factor. However, it's also reasonable to question why the driver did some questionable things.
For example, (and whilst I don't drive trains I do drive cars - and yes I know they are very different to drive but the laws of physics aren't) why when it was known that there was low grip that they didn't start to lose speed over a longer period.
In a car you assume a 2 second breaking distance to the car in front, unless it's wet and then you double that and if it's icy you double it again.
I do have a question, on the deceleration graphs there's a note about a 50mph PSR warning board, whilst one of the trains does go through at below that speed, the other two don't - is that a speed limit (in which case why were the other two too fast) or guidance (in which case or should raise questions of any driver which didn't follow that guidance who then was involved in an incident), a warning of a speed limit (again why not use that to start to slow the train with the lightest of break use, maybe even intermittent breaking, which appears to be what one of the trains did) or something else?
As I said, clearly without the trees things would be different, but in a lot of road accidents there's factors which make things worse than they should be (for example leaves blocking drainage) and whilst they should be the main focus that doesn't mean that people can't question the decisions of the driver (for example if driving a car on a road with excess water due to blocked drains, if you're approaching a point of conflict it would be good practice to reduce your speed more than normal, if someone didn't do that and then had a crash, it's reasonable for people to ask what were they doing?).
From what's been said, that's the tone of the posts about this (i.e. curious about their choices rather than, say, suggesting that the driver shouldn't have been driving). There's a lot of respect for drivers (you can generally ignore those who moan about how well paid they are, especially if it's about how they've broadly maintained their pay against inflation when others haven't) and this appears to be reflected in the tone of the discussions on here.