Think the point wasn't that Last Resort WAS a limited series, just that it SHOULD have been. If it was planned for 8-10 episodes and that's it, could have made it work. As an ongoing series, not sure how the premise was EVER going to work.
And if you sell it as a limited run, maybe you steal some eyeballs from the bigger competition, knowing it's a tighter story with a definite end, and that all 8-10 will air.
As an open series, going against big competition, guaranteed to have shit rankings and disappear soon anyway, unless it's ALSO a big hit. Not sure why you'd sacrifice something you think's going to be a big hit against a couple of the highest rated network shows, so ... ?