For asymmetrical Opens and Semi-Opens (i.e. when town has power roles but also VTs), you reach the problem that the setup is almost certainly breakable. That doesn't necessarily mean it's
townsided
; rather, it means that the players have to, from the start of the game, understand what optimal claiming strategy is in that setup in particular, in order to avoid being at a large disadvantage. Unsurprisingly, that's fairly unpopular on what's a mostly dayplay-focused site. You can normally work around this problem by using a Semi-Open where some subsetups are much more townsided or scumsided than others (e.g. F11), but then players tend to dislike it due to the possible lack of balance.The correct middle-ground, therefore, may be to find a setup which is low on power roles and where the correct claiming strategy is obvious. Vigilante + 6 VT versus 2 Goons, for example, is fairly balanced and it's also obvious how to play it claim-wise (the Goons fakeclaim VT, the Vigilante claims only when run up for a lynch). Again, that setup's been run more often in the Micro queue than the Open queue, but I can't see any particular reason why it shouldn't be in the Open rotation.
All that said, I suspect that the Open queue's real problem, besides the large overlap with the Micro queue, is that the rotation simply doesn't match what players are looking for. It may be worth gathering information about what specific setups people are interested in and what more general setup types people are interested in, and removing things that are unlikely to fill from rotation. (It's also almost certainly worth ensuring that we don't have high barriers to adding setups to rotation; "it's been run once and seems to work" is likely enough, we can always remove the setup again if it seems to be broken.)