The relatively low frequency and lack of early morning and late night trains between London and Brussels, plus the fact that a portion of space gets given over to Belgium - France travellers, and increasingly Eurostar were catering to London to Lille and even a handful of Calais stops, all strongly suggests that a 1000 seat 400m train is much too much for the route too. Of course, using a train which is too long for your needs and then still focusing your energy on the highest yield market is exactly the criticism of Eurostar I was making.
So....:
-Serving intermediate stops to make best use of train capacity and benefit more markets is the wrong thing to do, whilst
-Concentrating only on the highest yield markets is also the wrong thing to do?
I don't follow.