Were 100,000 of lives lost because of a delayed vaccine? Considering the third world hasn't had access to the vaccine and death rates are lower with delta I'm not sure skipping trials would have done much good.
Vaccine challenge trials are faster not because they are any less rigorous. They are faster because you are actively infecting people, instead of just waiting for participants to be randomly infected as they go about their lives. You can have a much higher level of reliability with a trial that is orders-of-magnitude smaller, and you can have definitive results within weeks compared to months.