I agree that new parents definitely need more support, and I wouldn't want anyone to suffer waking every 20 minutes for several years if there was a safe and effective alternative. That's why I try to raise awareness about the medical research surrounding sleep training, so that parents can weigh up their personal risks and benefits and make an informed decision .
I know it can be really difficult to make a decision about what to do and as mothers we often think - well, I will suffer this if it's good for the baby. If you're thinking like that, it might be useful to consider whether the sleep deprivation is causing depression, as maternal depression is linked with poor attachment and adverse effects on babies. So looking after your own mental health has a positive effect on the baby too.
You might also want to consider other risk factors, as PP mentioned falling downstairs from hallucinating. What is the risk to the baby if you crash your car, or lose your job?
The study you've quoted says that mothers report their babies are sleeping longer and that mothers' mental health had improved. I think those are 2 of the main things mothers will be trying to achieve when they begin sleep training, so that study is also evidence that sleep training does work!
We all, adults too, awake multiple times during the night, so you wouldn't expect a sleep trained baby to stop waking in between sleep cycles.
The aim of any sleep training is to withdraw sleep props that the baby relies on to get back to sleep, whether it's a dummy, rocking, shushing whatever. The aim is not for them to stop awakening; the aim is for them to be able to stay calm and drowsy and drift back to sleep naturally, by themselves, without requiring any sleep props - and so without crying and waking up the parent.
I really do recommend the Emily Oster book, Cribsheet, whatever concerns you might have about her conclusions, as she has links to lots and lots of studies on this topic which will give you a lot of Information if you prefer to do your own analysis.