I think the bot is incredibly useful. The criticism falls under a very specific group of users being very loud about their preferred source not ranking the way they expect.
Linking additional sources will improve it. Wikipedia maintains an active list and has an incentive to do so. Personally, I’d like to see a transparent methodology applied to a source: number of articles retracted silently, corrections issued in last 30 days, etc.
That having been said, I’d rather see efforts invested in other areas rather than inventing yet another “weighing” function for multiple ratings. Let us decide if mbfc is good enough or if we prefer ad fontes or Wikipedia or whoever. Give us two or three options and let us decide on our own.