I said that The Real Dr John specifically was overestimating the danger. He said "until they figure out how to fully shield the spacecraft, this is not practical for humans". And I really don't agree that "~5% increase in death rate" equals "not practical for humans". You have to put things in perspective: just the launch itself has a ~5% probability of killing the astronauts, so while a further 5% increase in the death rate is certainly not welcome, it is one additional danger of an already quite dangerous task. I think you'll find very few astronauts that refuse to take this risk.
That said, of course we need to reduce the radiation exposure as much as we can, because having astronauts who are dead, or with cancer, or with cataracts, or stupid, or with lung problems, or with heart disease is clearly not desirable. Going for extra shielding, as The Real Dr John suggested, is a terrible idea. You need a crazy amount of shielding, on the order of 100 g/cm, to significantly reduce the exposure, so waiting for that to happen is to wait forever. So I think the only plausible solution in the near term is to go fast.
In this respect I find Musk's proposal quite reasonable. He intends to do the trip in 90 days, and rotate the spacecraft to use to fuel tank as a shield during solar flares. NASA calculates that 5% from the 330 mSv in the trip would come from solar flares, so cutting that out and using the shorter trip time already reduces your pessimistic 1070 mSv to 650 mSv, so about 325 mSv per year, already well below the recommended level you quote.