I understand your argument and certainly agree that RCS consist of the sum of all parts therefore each part plays an individual role.
With that being said my argument was in regards to the enclosure itself on whether it gives a meaningful reduction to the total RCS of the 055 that justifies additional costs, additional moving parts, additional engineering and other overhead.
Nothing is free and there is no such thing as not having a downside.. Everything has a downside. The question is if it's worth it or in this case gives a meaningful reduction in RCS to make any difference. In my view there may be other things that may contribute in a more meaningful manner than the enclosure.
We don't yet know how stealthy the other parts of the ship will be.
It may well be that the other parts of the ship (despite its conventional flared hull design) will be stealthy enough such that having a stealthy gun shroud is a sensible design choice.