Indeed, their decision may have been partly influenced by the worrying improvement from the teams around them.
Leeds are the sixth bottom-half club to change their manager this season. And of the previous five teams, four have seen an improvement.
When Aston Villa ousted Steven Gerrard, they were only outside the relegation zone on goals scored, level with Leeds on nine points, from 11 matches.
When Wolverhampton Wanderers dismissed Bruno Lage, they were in the relegation zone, with six points from eight matches, three points behind Leeds.
But Julen Lopetegui oversaw a crucial 2-1 victory at Everton on his league debut, and among their last three league matches Wolves have beaten relegation rivals West Ham United and won 3-0 against Liverpool.
Those results have taken Lopetegui’s side out of the bottom three, two points ahead of Leeds.
Now Everton are suddenly looking similarly rejuvenated under Sean Dyche, who halted a three-match losing run, winning his first match in charge on Saturday.
Beating leaders Arsenal 1-0, the Toffees moved level with Leeds on 18 points, leaving the Whites outside the relegation zone on goal difference alone and perhaps precipitating their own move for a new boss.
AFC Bournemouth also saw immediate benefits after making an early change in August.
But O’Neil has since struggled to maintain that run of form, with his side having dropped into the relegation zone.
While O’Neil still has a better points-per-match average than Parker this season, Parker could point out his three defeats came against Manchester City, Arsenal and Liverpool, while he won his other match against Villa.
AFC Bournemouth’s time under O’Neil will serve as a cautionary tale for Villa, Wolves and Everton - that early gains with a new manager can quickly be lost.
Meanwhile, Southampton have so far fared worse under Nathan Jones than under his predecessor Ralph Hasenhuttl this season.
Saints were 18th when they made the change in November, with 12 points from 14 matches. They have now dropped to the foot of the table, with 15 points from 21 matches.
Jones is averaging exactly half as many points per match as Hasenhuttl was this season.
But the club backed their manager with a new contract and are now the form team in the relegation fight, with four wins from seven matches.
But after opting for a change this week, Leeds are looking for their own Emery, Lopetegui or Dyche.