I think a lot of people forget student loans in particular.
I also think people don't grasp the impact of the tax free allowance.
But I feel a bit different about childcare, in that I don't get any free chikdcare as I don't have children the right age so it's not something I factor in when thinking about earnings.
I also think than the 5% pension hasn't disappeared. It's still yours.
I didn't even include student loans or pension payments in the calculation of the post you quoted, just deductions for income tax and NI.
With childcare it's not just an issue for young children. It's an issue for older ones, too: if you earn over £100k you cannot use "tax free childcare" for a 20% discount on after school clubs, holiday clubs, nannies, childminders. Whereas a couple each earning £99k can get this 20% discount. Even though the lone parent will likely have far higher childcare costs because they cannot alternate caring for the children with the other parent while one parent works.
A couple each earning £70k receive child benefit. A lone parent earning £100k does not.
The couple can earn £24k tax free, the lone parent is taxed on all of their income. The couple can earn £100k before they even start paying 40% income tax whereas the lone parent is taxed at this higher rate on everything over £50k.
The system is ridiculous and makes it so that a lone parent with two children in childcare has to earn over £150k to have the same net income after tax and childcare that a couple receives if they both earn the average salary of £35k. I.e. they must earn twice as much, as well as having half as much time to earn/ care. There is a reason why other countries don't structure their tax systems in this manner to compound disadvantage deliberately.