Even if JP Morgan is correct, understand that the implied timeframe of their prediction is 10-15 years. Do you expect to pass away by 65? 70? If not, then your timeframe is much longer than theirs. And market performance tends to flatten out with a longer amount of time, like any average.
And, they revise this 10-15 year projection *every year*, so even they don't believe they will be correct, this time.
If anything, take this sort of information to mean that sequence of return risk is real, and if the current inflation then leads into high interest rates (to tame it) that type of scenario is what occurred to set the 4% rule. So study up on SORR, and perhaps enter retirement with a cash cushion, going part-time instead of quitting fully, or any number of measures to get you started.
But that period, in the late 60's leading into the 1970's, was double-digit inflation, with high unemployment. So, the words are the same, but it's kind of like a magnitude 3.2 earthquake: scary if you've never felt one, but barely noticeable if you have experienced a *real* one. If people are paying 18% for their mortgages, then we might need to really get worried.