No it's not false economy. False economy is paying premiership prices and wages, and not getting there - then you're in the shit. If some of your players aren't good enough for the prem, you sell them - for a profit! Win/win. Is it false economy for Cardiff if they sell Mason? I wouldn't say so.
If they're not good enough for the prem, and we do get promoted, we simply sell them. Getting there isn't easy, and it isn't cheap. We should focus on the best players to get us there, at the right price.