"No, I strike a blow to my body and make it my slave so that after I have preached to others, I myself will not be disqualified for the prize."
1 Corinthians 9:27
Yes Paul is 100% suggesting that most failed or to quote Paul
"Nevertheless, God was not pleased with most of them; their bodies were scattered in the wilderness." 1 Cor 10:5
Paul is saying simply do not take things for granted. Grace is given for a reason, not to be squandered.
"So, if you think you are standing firm, be careful that you don’t fall!" 1 Cor 10:12
It is like someone paying for you to go to university and learn how to be a good doctor.
You go to the university, play around and start murdering and exploiting your patients.
Paul is making the case though we have grace, we are called to behave and act a particular way, to see reality as it really is, and be ultimately responsible, sensible, good people. If this does not happen, then the gospel for that person is meaningless, and empty and judgement will fall.
It would have been better for them not to have known the way of righteousness, than to have known it and then to turn their backs on the sacred command that was passed on to them. Of them the proverbs are true: “A dog returns to its vomit,” and, “A sow that is washed returns to her wallowing in the mud.” 2 Peter 2:21-22
People do fall away, get lost in the world, loose the light. To suggest this does not happen is both not biblical and not the experience we have of people.
I would suggest you look at the prosperity gospel preachers, and one I know very well, who though I would have said in the past knew the Lord, certainly worships a different God to me. But how could this be, unless spirituality and eternity are different than we first think, and few literally find eternal life, though many partake in the blessing.