I disagree. If Sons finished 9th and stay up by winning the playoff, but go out of every cup competition early it'll have been a successful season only in so far as success being measured against the singular goal of staying up. There'd be so few wins witnessed it would be enough to make one question why they're so desperate to see the club stay up at all as at least a league down there'd be more wins available.
However, if the club finishes 9th and wins the playoffs to stay up but also gets to the last 16 of the League Cup, the same in the Scottish Cup and go a few rounds in the Challenge Cup, then you would be able to turn around and say hand on heart that it had been a successful season.
Staying up by a bawhair every season and doing nothing else of footballing note isn't success, it's subsistence. In decades to come it won't be staying up by a narrow margin that fans reflect on, it'll be finishing 5th, playing Aberdeen in the Scottish Cup latter stages, promotions, title wins etc. Success can't simply be 8th place every year, that's purgatory, not success.