I have not been a very active hubber mainly because I spend most of my time writing content for clients. I haven't made much headway here as far as earnings are concerned, so am not very sure if my response is right.
In my opinion, when you write for content writing sites, you earn a fixed income, at least you know how many articles you are likely to write in a month. But a steady income on hubpages depends on several factors like good content, traffic and clicks. Of course, patience and perseverance are key to success here.
I don't think that you can compare the income from 100 hubs to that from content writing. Hubs will fetch you a good income in the long run whereas once you start working as a content writer, you can make money immediately.