Do you want management jobs done by
(a) highly skilled, competent and experienced people who add value and make a difference, and understand the impact of what they can achieve
(b) people who would like to be all that, but in a competitive selection procedure never manage to convince a recruitment panel that they could actually get the job done.
Because anyone who is in category (a) and functioning at the level that is needed for these jobs is perfectly capable of getting a job paying £60k plus. For them, a salary of £50k ish is a step down, which they are probably doing out of a genuine belief in the principles of the NHS. There's only so far that you can stretch that good will though. If the choice is between a £40k position where your skills and experience worth £60k are that undervalued and underappreciated, or an equivalent private-sector role with a decent salary, then there comes a point where the lower salary is just too low. You have to have some self-respect. tbh even at £50k there are probably a few people in category (b) - not all NHS managers are brilliant, but the lower the salary, the more (b)s and the fewer (a)s you get.
There are plenty of £40k roles out there, which have a lower level of demand for skills and experience than these roles and are filled by either people whose level of skills and experience are appropriate for those roles or by people who are on their way up to more highly paid jobs once they have developed the necessary skills and experience. If you pay these kinds of NHS roles at £40k ish rather than £50k ish you will naturally attract a lower calibre of personnel, you only get to appoint the people who can't manage to get a job elsewhere, and the whole NHS suffers.
As PP point out the Art role is externally funded - but Art projects aren't a frippery. Someone will have done some serious research and made a valid business case for why a creative and art-filled hospital is better for patients and staff than one that has no art. That business case will have laid out the costs of creating an appropriate budget and management personnel to administer it, and compared that to the cost of the lower morale and longer recovery times which you get in a miserable hospital without such projects, and will have also compared the impact to what you could achieve with one more member of front-line staff instead, and the project was approved.
Of course nurses and doctors should be being paid more too, that is why the NHS needs more money, but an NHS without competent managers doing the administrative side would be even worse.