Based on the OP's careful description of the "dent" --- "It is about 3/4" and very shallow, just an indentation, maybe not even a dent" --- and my years of experience and expertise. As you and I agree, there are no absolutes, and ir might crack. So it's strictly an odds play, but so is bicycling in the first place.

BTW- I've personally suffered a D/T break at the BB, (aluminum frame) with no consequences except having to walk, and witnessed a crashed and buckled D/T le go at the head in slow motion, and again no crash. BITD we all rode compromised steel frames much worse than the OP's including crash buckled D/T which were the most likely to fail, but failures weren't common, and injuries from these failures even rarer.

But, you're right, that no one was ever hurt by not riding a damaged frame, nor an undamaged one either. So we can always just say "don't ride it" or we can make an educated guess of likelihood of failure and/or injury.

There are no guaranties, but that's always true.