Betty,
There's a balance to be struck. One-trick ponies aren't good. On the other hand, there's also a problem with what our German friends called Tornado at one point - der Eiergelegende Wollmilchsau (egg-laying, wool- and milk-producing pig).
P-8A is ASW, maritime patrol, overland and littoral ISR, missile- and mine-toting ASuW, SIGINT, platform for big-a$$ radar. Great, if you can afford it, but I suspect in UK service it will be carrying body length, extra hardpoints, big gennys and a whole lot of other heavy kit that doesn't get used.