Is that true? Sounds as if it could be. I don't think I've operated AM more than once or twice, mostly just to test something. Seems to me it's a mode that requires a lot more than barefoot power and modest antennas.
I have DSB and never used it. On my list of things to try. But for now, I wouldn't know when I'd even use it over "regular" SSB.
Only if the receiving station is using DSB synchronous detection. Otherwise, it's a waste of transmit power.
BTW, pretty much all modern amateur SSB transmitters use a DSP to generate SSB. First a DSB signal (or more precisely, a series of digital values at some sampling frequency like 24 kHz) is created and then the DSB signal is run through a Hilbert transform to eliminate one sideband (this is also called the "phasing" method when analog techniques are used).