If the capacity is only going to be 52,000 then the number of corporates/hospitality seats will have to be lower than the 5,000 that appears to have been in the original scoping -- and therein is the predicament.
What doesn't appear to have been fed into the decision over capacity is the 'new stadium effect' which has occurred at all new grounds and at all levels of football. Leicester City is one such example. In their last season at Filbert St the average gate was around 19,500, a fairly typical average for them. Since moving they have never had a single league gate below 20,000 and the initial uplift was of the order of 20%, a figure matched at many new grounds elsewhere. So even factoring in something like a 15% uplift at BM on the non-corporate/hospitality capacity at GP takes the absolute minimum new capacity requirement to around 45,000. The corporate capacity then takes it 50,000. And that's before allowing for the current excess demand for tickets -- even with a team that has won nothing in 23 years!
There is a view that the lower than expected capacity is a consequence of access and transport issues. But if so then that's been a somewhat belated realisation and so is surely an unlikely explanation.
I prefer one alternative explanation, the one in which the current controllers of Everton Football Club are seeing the new stadium primarily as a catalyst and a massive investment opportunity for the development of the whole north area, a development in which Moshiri, Usmanov, and other associates of extreme wealth would then hope to lead from the front in the attraction of the necessary investment. On this basis the actual capacity becomes of relatively less significance.