The only way somebody can upload that many listings is via the spreadsheet. As I already said that defaults to OnFirstBid for more than 500 items at any one time.
Even if a large lister uploaded 499 items a time (which would take a great deal of time,) they are extremely unlikely to choose anything other than RunTiLSold for the majority of their items, because they wouldn't have the time needed to keep on top of the constant updates required otherwise.
Unless a very large lister paid for featured their items do not dominate search.
If you look at the results given when making a search on eBid you will see:-
1) featured listings in time order.
2) countdown listings, (doesn't matter if they are an auction or BuyNowOnly or auction & BuyNow) they are listed in the order of the time they have left.
You cannot post 1 day listings here, the shortest time is 3 days, so nobody can hog the results that way.
3) RunTilSold
4) OnFirstBid in time order, so a 3 day OnFirstBid will show before a 10 day one. They only start to countdown once they have had a bid,
obviously if they are OnFirstBid buynow, they never countdown at all.
Not sure about the closing auctions on the frontpage, but in the ones at the side of the forum are restricted to showing one item per ID, so large listers cannot hog that either.
That is why we advise small sellers to use mainly countdown listings with reposts, to make the most of eBid search,
but, with at least 7 days to run, (& a BuyNow price as well,) to get the most out of the google product uploads.