While I don't disagree that its a little bit far fetched to say the two are equal, I don't think it is as far off as you say. 3 points:
- you are comparing a GP or specialist surgeon (average age... maybe 45-50) with a 'plumber I' (average age... maybe 25).
- Plumbers do a lot of cash-in-hand work that will never be declared as 'salary'
- Pay for tradespeople can vary enormously from place to place. I have noticed living in the UK for instance that tradespeople there earn far less than they do on average in the USA or Australia.
- you are comparing a GP or specialist surgeon (average age... maybe 45-50) with a 'plumber I' (average age... maybe 25).
- Plumbers do a lot of cash-in-hand work that will never be declared as 'salary'
- Pay for tradespeople can vary enormously from place to place. I have noticed living in the UK for instance that tradespeople there earn far less than they do on average in the USA or Australia.