Pay comparison doesn’t add up

REGARDING AW of Gosforth’s letter on whether it is easier to live within your means on gross annual pay of £18k or £80k.

Looking at the 2017/18 benefit to the treasury, a worker on £18k would pay tax and NIC of £2,480 and their employer would pay NIC of £1,357. The worker on £80K would pay tax and NIC of £25,823 and their employer would pay NIC of £9,913.

If both workers had a student loan, the worker on £18k would repay £60 and the worker on £80k would repay £5,640 pa.

The worker on £18k, depending on their circumstances, would probably qualify for in-work benefits and help with housing costs. The worker on £80K would probably have a mortgage which would have to be repaid from net pay.

As both workers would have very different jobs given the pay disparity, why the comparison?