Well as someone who buys art assets for no other reason than to see how something was done my opinion is most assets available in the Epic market place is targeted more towards the ideals of what makes for a “game” asset that no longer applies in a environment like Unreal 4 soon to be Unreal 5. Most noticeable is the lack of fidelity of the asset in favour of performance over the need for studio grade output.
As a member of a Indy team though what we are on the look out for is products that works with in our character development platform rather than characters and props that are unique as to their use. To facilitate this need we optioned Daz Studio and licensed for use the Genesis framework which to manage our character art assets and props and built the necessary structure.
I mentioned this as the two, DS and UE4/5, is actively being improved and art assets developed for the Epic market place that works with the Genesis framework also works with the Daz3D market place so that gives you two platforms for your art products. Toss in the Unity marketplace that would make it three.
Of interest
That said I would be more of the mind to make products for the Genesis framework as your products would have a longer shelf life over assets made just for the Epic market place.