The reason why so many people are having problems switching from DLA to PIP is that the goalposts have shifted. This is seen most in the mobility award, where specific distances are now the rule. It has to be said, on DLA, some folk with motability awards could walk a sight further than 20m. It matters little if you think that's unfair, those are the rules. You won't get higher rate mobility if you can, whether that is with sticks or not.
Similarly, with daily living, each question on the form scores so many points. If your point score doesn't reach the higher level, you'll either get standard rate, or in some cases nothing at all.
This makes assessing the degree of disablement fairly straightforward. And those same standards are applied in mandatory reconsideration, and also in appeals.
It should be remembered that these awards are not meant as income replacement, they reflect the additional costs of being disabled- employing a cleaner once or twice a week, or using a taxi for the weekly shop.
For info, I've just been awarded enhanced rate mobility and standard rate daily living. Just in time - I'm 65 in January.