Watchman is just not built for PvP.
Save pounding solo on a double healed Op, you just do not have the opportunity for the DoTs to do their work, as fights do not last long enough for them - not to mention the ability to keep your stacks so the DoTs are even more useful.
Single target damage has to be high DPH, or high burst within a 3-12 second window to be optimal/truly effective. Watchman relies too heavily on longer fights due to both DoTs and Stack issues to be effective (not put numbers on the scoreboard, but be effective to the field). Add in the ability to cleanse and vs smart opponents, this spec is dead in the water.
I have a guildmate who swears that Watchman is much better for 1v1s or defense, and myself and multiple others have been proving him so wrong since Friday, he's finally learning to utilize combat better and actually learn focus spec.
Sure, you can use it as is - and you can troll regz all day in it, but it's not as effective as Combat or Focus due to the design principal of the spec. In talking with SLC, I do think you could decrease the tick time in PvP (IE, same damage, less time it takes to get the damage done), and do something about the stacks (they last longer, whatever) and make the spec more comparable in PvP.
But at the same time, Im okay with this. Watchman is good for tank and spanks, Focus is good for aoeing trash/PvP. It's a balanced class even if the specs aren't balanced across the board.
I used watchman for ranked PVP back in patch 1.3. It was definitely viable back then. The dots actually tick very strong. The dots aren't the problem. TBH, almost no medics on Pot5 cleanse dots. Cleansing dots is usually a waste of time, since a heal could be being channeled instead, and watchman's dots reapply super fast.