By wearing Tia sorc staff you can get p1's + draught for p2's.
By stripping greater divining aug and putting it on gear you can get p2's and draught for p3's.
Personaly I see little reason to take divination focuses on a sorc, but PWK is still awesome to have.
As for 4-5 monsters, well ofcourse it depends how you determine the use, but there's at least 11 enemies that I can quickly think of which it works on, could be a few more that I dont recall offhand. Now many of those are trash anyways or can be killed with other ways too, so one might say there's 4-5 valid targets, but killing without save is always easier than using DC based spells.
I'd have propably concidered taking extra spell known 9 instead of water brieth to get PWK, but I suppose it comes down to matter of flavor. Your sorc always been on tough side to kill, built in waterbrieth will further increase that.
Not critical, but about 10% of abyss is underwater, abos is all undewater. Now for someone who has access on PW ring waterbrieth isnt really a proble at all, but even them can use other rings on those places if taken the feat. I took it aswell on my Pariah, how ever barb CC pariah doesnt get option for extra spells known or paragorn spell knowledge, which means they are far more limited in paragorn feat selection.