I believe that the research is absolutely valid, especially if you follow the underlying investment advice. If you put 50% of your "stash" into 10yr govt bonds at less than 3% return, you will have a hard time beating inflation if the assumption for inflation stands at 3%. If, on the other hand, you understand that treasuries are not a great place to park your money unless your stakeholders demand absolute safety, you could get almost as much safety by investing in a basket of corporate bonds and almost double the return on your bond portfolio.
Another assumption to challenge is the inflation number. When returns are expected to be low, inflation is likely to follow suit--look at the inflation numbers since 2008, they have surpassed 3% only once. If inflation were to rise, so would the treasury rate as we know our central bank loves to manipulate the treasury rates to fight inflation.
If you only need 3% of your stash to retire, it probably also makes sense to have a far more aggressive portfolio, and hold whatever reserve you need in cash, near cash, or investments that are far less volatile, like real estate (unencumbered of course). Another way is to purchase some deep out of the money protective puts on the stock portfolio, which may cost less then the opportunity cost of holding 10yr treasuries.
Again, the big problem with this research is that it assumes that the individual investing the money cannot think of any appropriate hedge to systemic market risk. Most of us can and do--even unwittingly do this.
The most important insight is that no one has yet been a great predictor of market returns, as most of the predictions are backward looking, or fail to consider all the macro trends going on in the world. I think this research falls into the same trap. What we all need to do is ensure that within our investment strategy, we have thought through how to act in the worst case scenario--and understand that markets change rapidly, so a loss of 50% today, may not take too long to recover if we have prepared for such a storm.