There is a large segment of roguelike players like Arseface who believe that single player games don't need perfect balance. That said, I do want there to always be multiple effective ways to approach the game and succeed, and I believe that to be the case, though some may be still harder than others.
Like Arseface says, having allies generally makes the game much more difficult, so you should be right at home with the desire to solo it; that's the safer strategy. Don't think that having friends would make things easier--unless you really know what you're doing, they cause more trouble than they're worth in the long term. (In the short term it's easy to feel like your little army is unstoppable, but that's before they start sending in assault squads to put you in your place. Try it and see =p)
Even more strategies will open up later as more maps are added! Some for those who prefer allies, and some for those who prefer solo runs.