I think the Police Federation are wrong, at the end of the day they're unhappy that they are having to change their culture at a faster rate than they're comfortable with.
I agree it's good Dick has been forced out, if she had any honour she would have resigned at the time of one of her serious failings and errors of judgement, for example allowing an off duty officer to abduct and murder a random woman.
The thing is though, Khan has to shoulder much of the blame too. If he'd had any sense he would have forced Dick out long before now. The failures of rank and file policemen are Dick's failings, but Dick's failings are Khan's failings.
Some of his cock-ups are just expensive and irritating, like his dismantling of the transport system, but others are tragic such as the Everard murder.
As Sir Kier Starmer has said, the man at the top is the man whose head should be on the block, and if Khan had any decency he'd be out the door along with Dick.