I'm not entirely convinced that LeopoldPhilippe is not a pseudo-random word generator browsing a historical dictionary and spewing PoDs onto the board; has he no opinions of his own?
(Is he in fact a non-Western academic trying to set questions in European history for his students, from a position of almost no background knowledge of the field?)
Anyway, as NAM Rodger points out, the castles that were actually built were basically white elephants. What Welsh revanchism they deterred is hard to estimate, but there was considerable pushing back, several of them were besieged and cut off, and had to be resupplied and supported at great expense and with considerable naval effort.
Supposing Edward I Plantagenet to be a bit more nautically minded, a good reason for him not to build a chain of castles is exactly that; almost everything worth controlling in Wales is on the edges of it anyway, within striking distance of the sea or the English land border,
the forts are going to need sea support, so why not save money (and they were bloody expensive) and build far more modest harbour- protection forts and depend on an english navy royal to police and fleece the Welsh?
Edward III had a head for the sea, Henry V did; ominous names for England's neighbours. Supposing the same sort of taste and talent for expeditionary warfare to have existed a couple of generations earlier, then what?