The vendor thing is rediculous yes. It should change to a way lower number for sure. But also keep in mind that by grinding in different spots with more major drops this speeds up a little. So the grind time guess is bit off.
With about the same overlvls as Landru I did a good amount of them if not most by grinding only itself. With the stuff I got from it and barely the 25k destroy achievement I am getting around 20 eff shards from this. But that is by shard farming constantly whole and half days for months on one of the best shard places. Which almost no one will ever do.
Somewhere around the 500 to 1 ratio sounds reasonable. If the devs find that too easy then at-least still lower it by a bit more then this crazy high 3000 to 1 ratio.