On Delta the Basic Economy (E) basically are standby since you can't select your seat and are only assigned one at check in (or at gate? can't remember). It's not even that much cheaper than regular main cabin.

I wouldn't expect it to be much cheaper, as involuntary bumping is extremely uncommon.

According to the article, 4% of planes are overbooked. And if they are, <5 will usually be re-booked. Which is a low single-digit percentage of passengers. So your chance of being denied boarding is probably <0.1%. Wouldn't say that all tickets are standbye.

It's rather that thanks to the internet we know of stories like these. 10 years ago no one would've known.

I say that you're "effectively on standby" when there's a potential for the overbooking to keep you off the plane, which is the kind of risk that should be made explicit.