It is too bad that they have not been able to play well enough to deserve promotion to another league. A few years ago it looked like they might actually become a major club but the sure have gone down hill. In fact they started going down hill when Sean stepped away as director. Maybe they need his 'mojo' to get back on the winning track.
They are a major club, najin - they're just not a very good one lately. They 'deserved' promotion this time around, but they didn't make it - by a single spot kick - and you get what you earn, not what you deserve. It's kind of like the Rangers in Scotland. The players and coaches are the same ones that have been in the Scottish Premier league for years and years - but because the administration and owners screwed up (royally and then some), they are paying the price - first by being dissolved as a club and now, reformed under a new owner, at the bottom of the third division in Scottish football. As far as the players go, they're still a major club.
Historically, the Blades have spent the vast majority of their existence in the top two flights of English football - since 1889, sixty seasons in the top tier and forty-two in the second level - only six years in the third (where they are now) . . . and one in the bottom.
From 1989 until last season, they were in either the Premier league (top division) or the Championship (second level) - granted, most of that was at the second level, but they weren't languishing in the Sunday leagues!
As far as Sean goes - I think, unfortunately, that long memories and a willingness to believe the worst (and a fair bit of jealousy on the part of some) precludes his ever being accepted again as a director - by the fans, anyway. He's better off staying in the terraces.