I am obviously very bad at explaining myself. Mind you
@llgon seemed to get it.
There are 2 tax advantages touted for pension provision.
(1) Tax free growth. In your example that would have given 24k in retirement for 6k investment on its own. Why have you interpreted this as 24k before tax?
(2) Tax relief on contributions, which is really only tax deferral. In your example that would knock 1k off the 24k. It is actually a negative feature - no thanks. That is what I mean about this aspect being an illusion.
Michael is actually taking the mickey here. (did you see what I did there?) He has appeared to be the fountain of generosity in giving 4k upfront and has some advisors waxing about what a nice man he is. He knows that he has only loaned the 4k and gets it paid back with 12k growth plus a bit.