Maybe the worst in the Premier League, although that Derby team of... whenever it was... had a much more desolate feel to them IMO.
Saints have been terrible, but they've also had a fair bit of bad luck with late goals and so on.
If you want REALLY bad, check out Brechin City in the Scottish Championship (the second tier) in 2017/18.
League matches: played 36, won 0, drew 4, lost 32, scored 20, conceded 90, finished on 4 points, all of which they got at home. Not a single away point all season.
They went down and then got relegated again the following year 2018/19. Now in the fourth tier, they finished bottom, but were spared relegation out of the SPFL in 19/20 because of the covid-shortened season.
In 20/21 they finished bottom again and were relegated out of the SPFL and into the Highland League where they remain, despite having won the league 2 years later - they missed out on promotion on penalties.