The Custodian has perhaps indeed more then CG weaponry but I am looking at it from a modelling stance & hitpoint value which classifies something as a Grand Cruiser. Mass wise it is less then a Repulsive.
Well, it is 45* so you need to convince a majority why it should be 90*. So far you didn't succeed.
Protector: because I know this vessel by heart. Name me one ship at 185pts that can do a alpha strike like the Protector.
It has 12 Railguns (or even 10 or

with 2 Ion Cannons as direct fire.
The Lunar can only do 6wb+2 lances at shorter range.
The Murder only has 10wb at same range.
You underestimate the 90* turn by a very large margin. This is an effect already taking place long before the lines come to pass. Especially in certain scenarios.In escalating engagement that turn rate is so friggin effective to regroup.
A cheaper Protector at 170 makes it only 60pts more then an Emissary without prow deflector. You think that's fair? By a large margin: No.
What then? Making Emissary better or cheaper?
The Custodian will even get less more then a Protector per point which you already complain about.
You see the problem?
Then the fact I tested a
weaker 90* Protector very often and it worked good & balanced.