The second example showed a tactic that I've been told is deliberate. Don't surround a suspect fully, let them move and keep a constant distance between you and the suspect. Against knives, this allows officers to build up numbers and keep the suspect distracted until the officers decide to act. They had tasers on scene, and guns would not have ended the situation any better.
The third video is a symptom of massive understaffing in the police. If they had had guns, they would have struggled to justify using them on any one member of that crowd, and against a large number of hostile but unarmed people, the police need numbers more than additional weapons. And they really do need the numbers, which is why I would prefer to see more officers and staff than more guns.
You probably aren't aware as he's not too well known, but the last two videos came from a very disreputable source. That youtube channel and the user associated with it have a long history of stirring up racial hatred, and of misrepresenting events to suit his agenda. When he's not in prison, he's usually producing misleading videos like that last one.
The final video is part of a demonstration that followed a pre-agreed route through London, and the police officers being filmed were leading the crowd through the city. They went past the place I used to work, and there were plenty of cops at the back of that crowd as well, making sure that the demonstrators kept on moving. It got violent, but only in sporadic outbursts, as many demonstrations do.