How high someone is paid is not proportional to how hard they work. There are extremely hardworking people and also a number of lazy buggers at every possible income level.
Salaries are set from a complex dependence on how the supply-and-demand market is balanced for the particular combination of natural talent, knowledge and experience needed to be able to perform that function well, how popular the career path is, plus the profitability of that job function.
Care workers and nursery staff are not low paid because they don't work hard but because people with the skills and experience needed to do the job are in sufficient supply that wages don't need to be any higher and in any case the system couldn't function of wages were much higher because the service users can't afford to pay much more so that won't change.
Investment bankers aren't working much harder but the talent, knowledge and experience needed to do it well is pretty rare and the banks need to recruit and retain the best talent because the most talented individuals personally generate millions of pounds a year in income for the bank and well happily take their talent to a higher-paying employer if offered so the market forces spiral their remuneration up and up. If your employers know they will lose millions of they don't agree to a request for a £30k pay rise then you have them over a barrel.
So yanbu OP - the justification for cutting higher rate taxes being linked to hard work is ridiculous but those saying it know that it's a lie anyway. The truth is that the Tories want lower taxes for the rich because they are funded by donations from wealthy donors and there is an election coming up so they need to Pay the Piper. Don't waste time analysing why liars lie or deconstructing the specifics of each lie.
I'd like to see a tax system which applied a "social good" adjustment at every tax band so that each industry and job function could be given a rating on a universal five-point scale according to how beneficial to society that work is. So nurses, doctors, paramedics, fire fighters, teachers etc get the highest rating, ethically neutral careers like software engineering, restaurant staff, and people working in retail get a neutral medium rating and those whose work is exploitative or damaging get a negative rating - arms dealers and polluters for example. It could never work because we could never get universal agreement on the ethics behind such a rating system
So a highly talented surgeon earning over £100,000 because the rarity of her skill and experience justify that salary pays the same tax as someone earning the same income working for an arms dealer (or probably more, as the latter will be fiddling their taxes) - and that sucks.