point was the arguement you made leads to a conclusion we could simply take everything to be "fair". after any tax the inheritor still has more money than those with no inheritance at all. also the example of child A & B is too narrow, we could have a hundred different scenarios of peoples...
should have 100% IHT then right, make sure no one benefits from someone else. probably want to tax gifts/loans too.
or we could have tax based around need to fund services, not to equalise contrived life experiences. child A could just as easy spaff the 50k on a car and holidays while child...
the reason for no CGT on primary residence (it is paid on second homes) is it would be grossly unfair to take large cut of someones value when they need to move. its only when downsizing or moving to a cheaper area that people see a net profit from selling their inflated homes.
ignoring those that may need to move for work, change of circumstance. they may not be realising a net profit as they'll be buying something else at market rate. funny how people want a house to be seen as home not an investment, then love a tax on the increased value.