Failing to reach the Champions League alters the whole tone of a summer.
That matters because Celtic's usual edge in Scotland is built on volume as much as quality. A team chasing multiple trophies cannot rely on a settled core alone. O'Neill's recruitment looks aimed at raising the floor of the squad, not just the ceiling of the best XI.
The timing is important. Other reports say Celtic are off to a perfect start in the league, capped by a 3-0 win over Aberdeen. Camilo Duran is also reported to have scored again, another sign that key attackers are already finding rhythm.
That combination matters:
Missing Europe often brings scrutiny, but it can also sharpen a domestic title defence if the squad is refreshed properly.
The next test is St Mirren on Saturday, and it should offer an early look at how quickly these additions can change the shape of O'Neill's side. If Celtic keep winning while blending new faces into the group, the conversation will move from deadline reaction to whether this revamped squad can turn domestic control into something more durable over the months ahead.