I get what you're saying WJ, and I could be wrong, but I think that even though Antz was the first to come out, POE was the first in production....? I know that before there really even was a DW, Spielberg asked JK what type of films he'd like to make, and JK said that he wanted strictly "epic" movies, so that's how POE was really born. (I think it was originally called "Moses.")
It was just my feeling, from what I know about DreamWork's early days and the "Ten Commandments/Terminator 2/Lawrence of Arabia" type of films they were planning, that CGI wasn't really part of the picture then, and really only became part of the plan because Toy Story did so well, hence DW buying PDI very shortly after.
Then after A Bug's Life did
really well and POE did acceptable but not stupendous numbers, the whole DW/2d epic plan was cast into even more doubt. It's really hard to say whether it was comedies that became more popular or CGI (most likely the former) but any which way you look at it, it cast DW/JK's hopes for "epic" films into even more doubt, at least from a financial standpoint.
Even as early as A Bug's Life, I think the DW rationale was: "OK, even though we're halfway into these serious epics, we've got to re-think all the serious stuff and make them more like comedies, because POE just didn't go over very well." And as time went on and more and more studios (Disney, Fox) were getting into CGI, DW had little choice but to follow suit.
After Sinbad came out and barely made a dent compared to Finding Nemo, the handwriting was on the wall. This was right when JK said, publicly, that as things now stand, "the traditional animated film" was most likely a thing of the past. Of course, it had to do with money--DW was in really bad financial shape then. You can argue about whether he should or should not have given up 2d just to keep up with Pixar's numbers--it's really hard to say-but one thing is certain, at least in my perspective--it was something he really didn't want to do. In all these interviews at the time, and later on even with the Shrek films, he said over and over again that it doesn't matter whether or not the artist uses CGI or 2d because it all comes from the same place no matter what. I really don't think that he believed any of it.
He always hated cartoony, exaggerated styles and now he was more or less forced to make films like that. (at least if you look at it from a strictly financial and not artistic perspective.) That's why some of DW's CGI films, compared to the 2d ones, often felt remote and lifeless, even though they did have some very good qualities. It just wasn't what DW was going to be. They had no idea what the prime directive would be after A Bug's Life did so well and Sinbad, El Dorado and Spirit did so poorly. Of course we all know what happened next--Shrek/Shrek 2 swooped down, did amazing numbers, and saved the company.
And Shrek--at least the CGI comedy with pcr's and adult jokes-- would more or less become the general template for almost every DW film after that. Despite its merits as a film, as well as the merits of Over the hedge and Mad and even SharkTale, all these films were produced because of fianancial need, not so much artistic passion. Most of it was left behind in 2d.