I can't speak to whether its hard leveling is in relation to other classes as I've only leveled a Sentinal and a Sith Assasin, but spec wise, if you don't go watchman it makes your leveling much more difficult.
For example I was taking on a story level boss as combat spec, no Two-man indication on the quest. I started out with me tanking then let T7 take over when I got low health to try to spread out the Damage between the two of us and still ended up getting destroyed by the boss. I specced Watchman and went back, T7 still died, but the boss easily died and I was still full health by the end.
Long story short, the other trees need a huge buff at least for leveling.