My test of tests is for a non-LI team to play the same game twice once with LI, and once with whatever other tactic, and see if the can actually only win by not playing LI. Always I saw that even a team good at other offences was still better at LI.
Last season I didn't run Princeton or other outside offenses nearly as often because of concerns over GDP. Late in the season I picked up a very high IS player (especially compared to my other players) and ran LI in the playoffs. My team shot under 5% from the field in the first quarter and never really caught up - the 18 IS guy ended up shooting 20% from the field that game. Thanks to garbage time I cut the deficit from 21 to the final margin of 12, but I might be the one example of a team that did worse running LI than I would have with just about any other offense.
A link to my season on buzzer manager:
(http://www.buzzer-manager.com/calendrier/30851/?saison=28)Now, to be fair, I lost to the same team in the same situation a few weeks back when I ran Motion into his low post, but the deficit was about 7 points give or take a bucket most of the fourth quarter. And part of the reason was that they were a better team. But adding an 18 IS forward and running LI still ended up killing my offense in the playoff rematch.