The slow updates are due to Epic’s staff being too small to handle the amount of requests. This is something we have been complaining about for a while now. Email support is the same (I’m assuming you’re referring to marketplace-support@unrealengine.com?). It takes weeks just to get a response some times, and then more weeks for action.
I have actually decided to put future assets on Gumroad until the marketplace becomes worth the 30% we are giving to them. Many other sellers in the creator’s hub are unsatisfied with how things are going and the amount we are giving them for a very lacking service It’s easier to give customers the experience they deserve on other marketplaces that don’t tie our hands behind our back and demand high royalties.