It's probably more light level than anything else. My take on the issue is that Legendary lost sectors have always been "accessible" relatively early in a season, and Bungie even added the seasonal challenge of completing one in Week 2, but the recommended light level is 30 above even the Powerful cap, meaning most casual players weren't anywhere near the point of feasibly completing one. My take on the solution - since there's already a Master level for lost sectors above Legendary, the light level for legendary should be dropped down to the Pinnacle cap of 1810, making the "lesser" of the harder lost sector versions more accessible, while still keeping the Master ones where they are now.