If PIP had to cover the ACTUAL costs of peoples disabilities, I can assure you that government expenditure on PIP would quadruple or more.
The idea of refunding or providing vouchers is hysterical, honestly - they can't manage to do the paperwork for a simple 'no I have not got any better, yes my lifelong, life limiting, incurable health problem is still lifelong, life limiting and incurable', inside 19 months!
Who on earth thinks they'll be able to turn around applications (because you sure as hell will not be able to, nor would want to, spend money without prior approval!!) for vital equipment, therapy, private treatment, in a time frame that keeps humans alive, in work where relevant, functional...
It would end up as in the US, with people arguing endlessly for equipment they've been told they need by a professional, that the desk-jockey says isn't on an approved list so they can't have, and waiting months or years for unsuitable alternatives.
If there are 'too many people getting PIP' then they need to look at why MORE people are disabled!
Fewer people successfully claim PIP now than claimed DLA, the aim of the change over was to reduce successful applications by around 20% even though the figures showed the fraud rate was less than 1%.
So if too many people are getting PIP that suggests too many people are genuinely disabled and need PIP and why is that? Poor health services, toxic work culture, awful government pitting the nation against one another...