Similar to what @ShmuelBrin said, but on more of a psychological level:
As brought by theyeshiva.net, The Maharal of Prague (Gevurot Hashem 61) explains what happened when the Jews left Egypt:
The Exodus of Egypt, he suggests, was not merely a political and geographical event, in which slave laborers were allowed to leave a country and forge their own destiny. It was also an existential mutation, in which the gift of freedom was “wired” into the very psyche of a people. With the Divine liberation from Egyptian bondage, a new type of person was created—the Free Man: The individual who will never make peace with oppression and who will forever yearn for liberty. The Exodus implanted within the soul of the Jew an innate repulsion toward subjugation and an inherent quest for liberty.
If G-d would have waited even a second longer to take the Jews out of Egypt it would have been too late. G-d could have taken them out later, but by that point they would never have been able to change their state of mind, they, and by extension us - their descendants, would always considered themselves slaves.
The "Free Man" of the Maharal could never have existed.
You can take the Jew out of Egypt, but you can't take the Egypt out of the Jew, so to speak.
As it was the Jews didn't feel truly free of the Egyptians until they saw their bodies washed up on the shore of the Red Sea, and even after that they complained many times in the desert that they wished to go back to Egypt. (In fact, if I remember correctly, this is one of the reasons given why the Jews had to wait a generation before entering the land)
So it's not that that was a single point of redemption, as much as it was the last possible time the Jews could have remained in Egyptian bondage and still be able to truly be free once they were redeemed.