I don’t think you’re being disingenuous. But challenge trials wouldn’t have sped this up for a few reasons:
1. They would be limited to a small subset of low risk people. Young people with no known risks. Not the groups who need vaccines the most.
2. Much smaller size would...

2....severely limit the ability to collect safety data. Efficacy endpoints are from ~200ish people but safety is assessed on all the trial participants.
3. Even if started in late July, they’d still have to delay challenge for at least a month after the second shot.

4. Hard to do controls ethically (and challenge trials themselves are ethically debatable). Very difficult to justify infecting unvaccinated people deliberately when there’s no rescue therapy.