Yep, rental cost should ideally equate to the interest cost of a mortgage, but never has.
Back in 1990 a house I owned and rented out for £550 a month was costing £550 a month mortgage (residential rates with BS permission to let, as long before BTL existed). But rents have in reality in large areas of the country got a lot cheaper now, that same house now rents out for £700 a month despite the house being worth £130k.
I bought that house for £35k and this shows that it should now cost £102k
https://www.in2013dollars.com/uk/inflation/1990?amount=35000
Not quite the 5x property increase people suggest is it?
It’s only the South that has got totally screwed.
Oh, and Income Tax is now far lower than in the 80s and 90s too - it used to be that the low band of income tax was 30% not the paltry 20% people pay now, and Sunak is talking of reducing it further too!