I believe there are airlines in SkyTeam that at their biggest hubs have three check-in areas: Sky Priority, priority, and general. Depending on what the ratio of E+ to E passenger-flights is and (probably more importantly) whether the airline offers priority check-in as a benefit outside of FF status. Delta's Silver benefits page says:
Diamond, Platinum and Gold Medallion Members may use the Sky Priority check-in lanes. Certain airports may have a dedicated check-in lane for Silver Medallion Members. At airports which do not have a dedicated Silver Medallion check-in lane, Silver Medallion Members are permitted to use the Sky Priority check-in lane.
Whether there are any Silver/priority-but-not-sky-priority check-in lanes left in Delta's network is an open question (I've never seen one, though I've read from time to time that such lanes were often less congested than Sky Priority, which is often even now more congested than the general lanes). It wouldn't surprise me if at various points in time corporate contracts with DL have been able to include "priority check-in regardless of status" as a benefit. Similarly, the priority boarding ("Main Cabin 1") for DL Silver/STE is also obtained just from having a c. $100 AF credit card or a ticket associated with a corporate contract.