This is how I play. Mainly cause I'm lazy and don't respec. But I do one fp a night with (short queue times) and then quests. Heroic quests will be easier to do too. It gets slow, but you can solo lots of elites and bosses. Since you have other characters, you can gear out your first companion with Adaptive Armor/Weapons and mods, makes it go a lil faster and improves his survivability.
It does not get fun when your companion dies and you have to solo a boss for example. Playing this way makes you depend more on companions and players than other specs.
Oh and I've leveled pretty quick (lvl 49 in less than a month playing nights and weekends only) but there was double xp weekend and bounty weeks provide a hefty boost to xp.