At LGW gate 55 is the same as gate 57 - thus 55 starting at A left hand edge is always domestic, and the K side is rarely (however I have had a domestic departure from bus gate 55K).

Similarly, 57 H is identical to 55H, for example.

In terms of domestic arrivals, the OP is right - it seems the bus is now taking you to a big staircase in the middle of LGW which is far better for connections rather than being good for arrivals.

The old twisty ramp was much better for arrivals, but hopeless for connections.

As for baggage collection time, I've only collected domestic baggage at LGW once, and it took all of 3 minutes from arriving at the belt.