The advantage I thought with Dartford is that the train from London Bridge terminates there and you can take all the time you need, plus the fact there are always staff available to help and lifts if you need to change platform.
It's one of these journeys where there are a few options and a lot of swings and roundabouts.
Lifts are often out of order
Which platform will it terminate ? (ALL on a curve)
The issue is with the gaps and mobility. Only knowing exactly which door to alight at will resolve that issue. Front coach at Dartford will not be on the curve and little gap. Back coach too but depends on train length still gotta walk the platform length. Only ramps solve both the issue with mobility and gaps.