I don't think you need "abnormally strong opinionatedness" or anything else special: all you need is a certain (long-term) dedication to the project and willingness to just put in the work.
Almost every project is an exercise in trade-offs; including every possible feature is almost always impossible, and never mind that it's the (usually small) group of core devs who need to actually maintain all those features.
I interpreted "opinionatedness" as meaning they have a clear definition of what sqlite is and isn't, including the vision of where it's headed. That would result in a team with very strong opinions about which changes and implementations are a good or bad fit for sqlite.
Can a project consistently make the right trade-offs without having strong opinions like that?
Almost every project is an exercise in trade-offs; including every possible feature is almost always impossible, and never mind that it's the (usually small) group of core devs who need to actually maintain all those features.