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Best ADZilean NA
Prospector's items only exist in order to make the health bonus a "unique" stat. In dominion, survivability is much more valuable than in classic because the protection of your towers is not nearly as dependable and the map layout doesn't allow for as many clean escapes.
Building doran's ring and blade in dominion would be the best way to get chunks of survivability quickly without sacrificing damage. If these items were allowed, you might often see boots + 5 dorans being built by many people through the first half of games out of necessity rather than choice. Prospector's items give us the ability to start strong but remove the advantage (and thereby the necessity) of building multiples.
Now for the point: It is not necessary to substitute a prospector's shield because the doran's shield gives ONLY survivability with no added damage or utility. Since the whole point of doran's shield IS survivability, it would be silly to make any of its stats "unique." Furthermore, tanks gain no benefit from building doran's shields anytime beyond the first fight at top anyway, so there is no need to change the item's balance.
This is why we do not and will continue not to have a "Prospector's Shield" in dominion.