Right, so chair a committee whose motions get voted down by the (majority) opposition (in scenario a above); or get negotiated away by the coalition partners who have a majority anyway (scenario b).
The tram funding and Calman commission episodes at Holyrood show what can happen to minority governments. Which is democratic in principle, but if the majority opposition is SNP/Tory/rump Lib Dem, how will Green pledges get through?
As for being the most junior partner in a coalition where the Tories have more votes: Westminster coalition should be caution enough, whatever Labour's good intentions.