Not a new truth but one emphasised by the array of talent on Manchester United's bench when set against an insurmountable depletion of Leicester's resources.
When O'Neill joked about borrowing some of the men Alex Ferguson had not called upon he was thinking about internationals whose combined worth would be around pounds 20m at today's inflated values.
For one reason or another, injuries, suspensions and sickness, Leicester had to take the field without Emile Heskey, Matt Elliott, Frank Sinclair or Andrew Impey. "All things considered we did very well," O'Neill said.
It is a phrase that puts Leicester's expectations - and those of most other Premier League clubs - into stark perspective. Through to the fourth round of the FA Cup and Worthington Cup semi-finalists Leicester are having a pretty good season but they can forget about ever being good enough to become champions.
Thrilled as O'Neill was by the effort his players put in to force the structural changes that Ferguson made at half-time (as well as delivering some stern words about complacency) Leicester could have been looking at a defeat in double figures.
Stretched to the limit of availability - "We were down to 16 players," O'Neill said - Leicester made a game of it in the first half but the encouragement of Theo Zagorakis's blasted equaliser lasted only until United raised their game to Ferguson's satisfaction.
Transferring Ryan Giggs from right wing to left midfield and moving David Beckham out wide gave United better balance but it was the burgeoning partnership between Dwight Yorke and Andy Cole that brought Leicester back to reality.
Yorke, who put United ahead when Cole dummied Denis Irwin's low centre in the 10th minute, finished with a hat-trick and Cole's two brought their tally to 30 goals for the season.
Since Yorke's arrival and the friendship they have forged, Cole has recovered the confidence and sharpness that was seen from him in Newcastle's colours. As with all successful striking partnerships there is a sense of telepathy.
The former Arsenal, Manchester United and Republic of Ireland centre- forward Frank Stapleton thought their combination stunning. "I knew something like it for a while at Old Trafford with Norman Whiteside," he said. "You get to know each other's play, how the other guy is thinking, the positions to take up."
Yorke - how Glenn Hoddle must wish that the man from Trinidad and Tobago was available to him - is an exceptional talent, not only skilful, quick and alert but impressively strong in possession.
It was Cole, however, who at last confronted Leicester with the enormity of their task, taking a through pass from Giggs to slide the ball past Keller in the 49th minute.
Leicester's spirit held but the roof was coming in on them. Yorke spun effortlessly clear of Walsh who had made the mistake of getting too tight with him and set up Cole for United's third.
Yorke got back into the scoring act himself by stealing the ball from a hesitant Keller before rolling it in cheekily from a narrow angle.
Leicester refused to give in. Walsh, who was sent forward, got them a goal and it was O'Neill's contention that another might have led to a dramatic conclusion.
Not a wild assumption in view of United's untidy defending and Schmeichel's continuing uncertainty but nevertheless ephemeral. Yorke ought to have completed his hat trick earlier than he did but it came after Cole had clipped the crossbar.
Jaap Stam completed the scoring with his first goal for United and Leicester's supporters were left to reflect on an ever-widening gap between the Premier League's elite and even those teams that are as highly motivated and astutely managed as their own.
Goals: Yorke (10) 0-1: Zagorakis (35) 1-1: Cole (49) 1-2: Cole (61) 1- 3: Yorke (63) 1-4: Walsh (73) 2-4: Yorke (84) 2-5: Stam (90) 2-6.
Leicester City (3-5-2): Keller; Taggart, Ullathorne, Walsh; Kaamark (Campbell, 71), Izzet, Lennon, Zagorakis, Guppy; Cottee (Fenton, 89), Wilson (Parker, 71). Substitutes not used: Arphexad, Oakes.
Manchester United (4-4-2): Schmeichel; Brown (P Neville, 46), Stam, Berg, Irwin; Giggs, Beckham, Keane, Blomqvist; Yorke, Cole. Substitutes not used: Van Der Gouw, Johnsen, Scholes, Solskjaer.
Referee: S Dunn (Bristol)
Bookings: Leicester: Walsh, Lennon. Manchester United: Keane.
Man of the match: Yorke