I doubt that in pure dirt-hogging applications that even a 299C or TL250 will outwork a 939C -- the buckets are bigger on the full-size track loaders. That being said, the numbers of 90 HP crawlers sold is pretty low. They are expensive to maintain relative to a dozer, and in Europe and North America, where the lot sizes continue to shrink, I don't think that the market would support more than one-hundred a year... owning the market (973) is one thing, but splitting it between two manufacturers (605D, 943D) would probably not be on Cat's list of priorities.
But that's just my take. Maybe the crazy engineers are working on a 943D as I type this.