‘Sarah’s scribbles’, ‘Fowl Language’ and ‘Lunarbaboon’ have a big online following which probably helped them to get (a) book(s) published with Andrews McMeel
I think ‘Books of Adam’ and ‘Owlturd’ are getting a book by them as well.
Of course, I do not know the details how these authors got their contracts, neither do I know if they created some extra works for their books or if those were all comics they already published online.
However, I’m convinced that a large following is a selling point when you pitch to publishers. After all, it’s an indication that your work is appealing to a sizable audience and could do even better with a proper campaing behind it.
In other words, go ahead and self publish online first.
If you can’t successfully pitch it to publishers, self publishing is still an option 