Seems to be an accurate summation. Taking into an account that Britain was a source of some valuable items and that soon enough Rome was willing and able to commit considerable resources to crush a revolt in the Judah, it is not quite clear to me why such a situation would happen short of the gratuitous combination of the disasters along all Roman borders. Of course, such a combination can be invented but it’s probability seems to be quite low (why not a meteor hitting the Rome?).So it seems that the answer to WI Boudicca won at Watling St is: she can leverage this to kicking out the Romans only if the Romans are distracted elsewhere.
Would that be an accurate summation? That a longterm win for Boudicca REQUIRES Rome to be prevented from fighting back?
On a strictly military side, it does not look like the Britons had been a formidable military power even if they would manage to win a battle with a numeric advantage of 20:1 (which they lost in OTL): choice of a battlefield and the tactical arrangements on the British side were pathetic and Bodica’s ability to exercise command during the battle were plain zero. The tribal mobs had been just rushing ahead and that was pretty much it. It is probably fair to assume that after the Romans are out, these tribes will go their own ways and by the time of the next Roman landing there is no unified state in any meaningful form.