Of course evidence is needed. I've been visibly physically disabled my whole life, but total disaster struck a decade and a half ago forcing me to later claim PIP if I wanted to continue working, now from a wheelchair and with a second layer of brain damage to work around. I'm seriously affected, but also very active and put myself through hell to get to there, but can't do half of it without a carer.
My PIP evidence is X-rays, MRI's, large amounts of hospitalization, and NHS consultants: neurosurgeon, cognitive neuroscientist, cardiologist, and gastroenterologist, and the specialist NHS hospitals I'm under. I've a collection of diagnoses relating to a wonky and damaged body and (NT) brain systematically failing. You can tell quite a bit from the collection of tubes and wires, and visibly misshapen bits from overuse of what works, and atrophy of what doesn't.
None of it means a dam thing though when I'm being 'assessed' by a large angry, aggressive, misogynistic, sports therapist standing over me covering me in spittle, shouting that the "consultants are wrong", I'm "misdiagnosed", and "even if not" it "doesn't affect" me much, as my GP doesn't believe in pain killers or sleeping tablets, and this man has no idea (or interest) what the rest of the medications are for.
He can see that in hospital I'm automatically on morphine and zopiclone from day 1 every time because of the level of pain I'm in and the difficulty of treating me when I'm self managing it.
He used it to say if the GP won't prescribe them, then it "proves" I'm "not in pain and unable to sleep unless hospitalized", and if I was in pain, I "wouldn't be able to work", and if I wasn't in receipt of an 'Access To Work' grant I "clearly didn't need help". (was actually in the very long queue before that also collapsed)
He "knows" because he's a "trained sports physiotherapist!"
That's the qualification good enough for the DWP to counter and dismiss all those highly trained consultants and their scans etc!
And just like that he struck me off from multiple high needs points, to insufficient points for any disability help to allow me to work.
(reinstated following formal complaint and importantly an illicit tape recording of his aggressive bullying.)
It really isn't about evidence, though when you have good evidence you tend to think it's why you've been awarded. Then you discover really it's it's about assessors, bell curves, and private companies making money from the DWP, and often good and bad luck in who you get, when.
Also regarding diagnosis:
Some time after I lost a year in hospital and was facing loosing my home through being unable to cover my rent and CT (no help available when in hospital) an incredible neuroscientist at the peak of his career, was hit by a car riding home from work.
Amongst other things, he was a Royal Society professor with a RS grant to develop his long term research program over ten years, and had family.
Part of his work was with 'neglect patients' and how others perceptions of them shaped neurological function.
He believed in people being able to reach their full potential regardless, and was making really important discoveries in the neuroscience world.
Absolutely not someone shirking or wanting to not work.
He suffered a complex dislocation of the knee, and after two bouts of failed surgery on it, was left permanently disabled with continuous excruciating neuropathic pain, and unable to hide it, or be able to work through it.
He went from the top of his game and a hugely useful member of society, to suddenly being seen through the lens of potential liar, scrounger, potential drug seeking patient, and a potential 'burden' because of a few seconds of (allegedly) someone else's carelessness.
Despite who he was, and who he knew, he didn't have any actual diagnosis beyond depression, insomnia, and PTSD.
I can see what the viccious'n'mean would have had to say about what those diagnosis's mean, and his right to 'tax payer' assistance to be able to manage a future life.
Sadly he jumped from a 60ft bridge rather than go through more, knowing from his patients exactly what the future held for him, and his fears about his employability and his fall from grace to becoming 'publicly distrusted' and a potential "burden" on those he loved.
He was someone very conscientious, admired, and respected.
"Consigned to an existence of permanent disability" and "subsequent mental anguish" and "ill prepared for societies judgement" where terms used by his peers.
Disability can happen to absolutely anyone, how people are treated when it does, counts hugely.