Attendance went down about 100,000 this year, and the ring year, 2018, was down from 2017. (We also missed 2 home games for going to London.)
Our attendance in 2012, 2014 and 2015 was nearly identical to 2013.
Sox fans will support the team. Most tickets are bought way before the season starts or is half over.
I'm not sure fans need to think we have a chance at a ring every year, but they want to see some sort of excitement (offense?) or a decent product, as long as there is a hope we are getting better. Seeing some fresh, young faces may not be all that bad.
I'm also not so sure a JBJ-less Sox team will finish 20 out next year. Now, if we trade JD, and some pitchers have surgery, then yes-maybe.
I may be different from most fans, but I'd rather see a shorter period of rebuilding, even if it means having an awful 2020 season. I don't want us to suck, but if we make some good trades for some top young talent, my optimism will overpower my dislike for seeing us lose a lot of games in 2020. If it takes 2 years to get back to a top 4-6 team, I'm okay with that, too.
I do agree with you on the mediocrity thing. trying to stay mediocre, while rebuilding, might just extend the time it takes to get back to the top.