Yeah I know. I hate Ubisoft's direction. I've played every AC and this is finally the one that represents my heritage so I wanted to get through it. I know if I reached a point where I had to grind 5 levels to progress I would quit, so I broke down and bought the boost.
After playing a while I think it might not be needed as long as you have the DLC and play them when you reach the rec'd level ( which are surprisingly low) maybe the XP you get from those DLCs would get you to a level that the grind would become less terrible toward the end.