Watson doesn't have a consistent offensive game but has shown a few flashes, namely getting to the basket and knocking down some threes (more than streaky here).
The reason you play Watson has more to do with defense, rebounding, and ability to play in transition. There is no reason Pavs should be getting minutes over Watson. At his worst he ducks at both ends and at his best he's mediocre offensively. With Ward hurt, it would really help the defensive continuity to have a guard that can guard multiple positions, get some rebounds, and convert on a few offensive opportunities.
I bet if you were able to play Pavs and Watson 15-20 mins a game, against the same opponent and compare performance Watson would win in a landslide. Pavs isn't athletic or strong enough to keep up defensively, isn't quick enough to play in transition, and is mediocre at best as an offensive threat. Many of our defensive break downs start with Pavs when he's on the floor. With Watson you get an elite defender, an adequate rebounder for his position, and someone that can give roughly the same offensive output/efficiency as Pavs. More importantly it gives you a + weak side help/rotation defender when Milan is on the floor. Having Pavsa AND Milan on the floor at the same time is a defensive nightmare.