Insurance is no different to anything else; you largely get what you pay for. Buy a cheap policy and quite often you can expect crap service. And then people whine about how unfair insurance companies are. Boo hoo
It's that old saying, you don't know how good your insurer is until you need them to pay out.
An insurer can rack up tens of thousands of ££s costs arguing who is wholly to blame. And in this day and age, a 100% at fault claim can cost them a hell of a lot more than the cost of repairs. That's why sometimes they're keen to go 50/50 - each insurer pays for their own insured's losses. In a 50/50 settlement, that's usually the cost of repairs only e.g. you can't sue yourself for whiplash and 8 weeks of Range Rover Sport hire
So even when a driver argues that there are mitigating circumstances etc, some insurers will still push for a 50/50 settlement. They'd rather pay out £4000 to repair a car than £8000 fighting a claim they still might lose.
Personally, I think the Mazda's insurers are going to have a job on their hands not to prove their driver was not 100% at fault. And that includes the damage to the other cars. From what I can see on the video:
'The Lambo was speeding'. Are you sure? What speed was he doing? Engine noise = speeding, err nope. What gear was it in? I don't think anyone has ever been done for speeding because of the noise of their car. The driver had nowhere to go and only a fraction of a second to react. Quite simply, the Mazda pulled out.
The bill to repair that little lot is going to be eye-watering so in this instance, I can see the Lambo insurers digging their heels in and refusing to accept anything other than 100% Mazda driver's liability. They won't be interested in 50/50 for the obvious reasons.
If I jam my brakes on for absolutely no reason and someone runs into me, it's their fault. You cannot argue it. Similarly If I expect someone to pull away from a roundabout and they deliberately stop to cause an accident where I run into the back of them, it's my fault, no argument (that's why the scam was so successful).
If someone pulls out at a junction and you hit them (and it's caught on video), it's going to take a miracle to prove they're not wholly to blame (as Tipex found, even with witnesses etc).