yorkie, upthread you asked me to clarify whether, and if so why, I think the booking engines are correct in offering itineraries via Ramsgate on these "direct" highspeed services.
My answer was that it appeared odd, but I couldn't say whether the booking engines had applied the routing rules correctly, as I didn't know which routing rules should be applied.
Now it appears that it's just a straight forward application of the "direct service" rule, and there is no overriding "first arrival at destination" routing rule which would mean that the booking engines are incorrect in offering these itineraries.
Accordingly, I say yes, odd as the itineraries appear, to me as a non-expert, the booking engines are correct in offering them and the reason is that they are allowed by carefully applying the routing rules.
yorkie, on this forum you regularly call out the instances where train companies misapply the rules and staff who you say don't understand the rules. So when you ask in the OP whether a customer should be able to purchase a St Pancras-Stratford ticket and travel on the 'via Ramsgate' itinerary, surely the answer has to be yes.
The cries of outrage that such a customer would be "exploiting a loophole" are misplaced. In fact they are dangerous. If you declare that an itinerary which is valid according to the rules, mustn't be allowed because it is "a loophole", where, exactly, would you stop? And who would get to choose what is "a loophole" and what isn't.
Split-ticketing, some may say, is "exploiting a loophole", isn't it?