Building the DUB hub could still be achieved by using the A330 family, the way I see it is that down the line, while capacity per flight might not improve, but the opportunity to increase frequency by using slightly smaller craft might lead to an overall increase in capacity. Also if there is an opportunity to increase frequency, this might improve the attractiveness of the DUB hub and pull more UK passengers away from KLM's more frequent flights? Bearing in mind that any more frequency increases are probably a wee bit further down the line.
Just my two farthings, others may disagree (of course).