There's several ways one could compare RG's operation with one brought back in-house.
But just to make any comparisons as appropriate as poss, I'd recommend spending 30 minutes at Kings Cross observing the operation in and around the RG site (on plat 8). Note the slow and systematic way in which materials and carts are loaded, marked up, checked out and trolleyed to each train, wait on platforms, are unloaded, trolley back, checked in, unpacked etc.
Meanwhile, observe the EC catering crews gather at the end of their next train's platform, just waiting. Though when they do have a train arrive, they move with some speed.
Then remember how it was - on-board crews had more duties to complete during their run, including more of the washing up and prepping.
Its a complex operation, but as EC (and other TOCs) employ so many CS staff, then there has to be many ways in which duties could be re-allocated which would still work, even during disruption (which is where a shore-based operation can be a benefit).