IMHO it's not that people took on more risk than they thought but rather that people do not appreciate what risk is. Stuff happens. Risk generally is rewarded, but the ride can be jarring.
The average 10 year returns for multisector and for intermediate core bond funds were very close as of today (May 3,
2020). Multisector: 3.65%, core 3.80%.
Take the same ten years through the end of 2019 and the averages are multisector: 4.87%, core: 3.81%. (All data from M*'s legacy graphs;
see here for 10 years through 2019,
see here for 10 years through today).
Over the long term, higher risk investments will probably do better, but when there are corrections or disruptions, they'll come down to earth faster and harder, bringing their long term averages closer to the lower risk investments.
My guess is that the "wealth effect" has something to do with people's reactions. High flying funds make people feel wealthier than they are; they don't factor in embedded risk. So when, as is inevitable, that risk manifests and the funds show themselves to be just somewhat better, people tend to feel disappointed. I'm suggesting that rather than feel disappointed when bad things happen, instead feel just a little less good when good things happen.
Based on the performance figures, ABNDX is an average fund. It's done very well this year on a relative basis, about 3.5% above category average. And that's brought its 10 year performance up to about 0.35%/year above category average.
On the other hand, PIMIX has held up relatively well a
gainst its category, ahead 0.5% YTD. Even from peak (Feb 23) to trough (March 23) it did better, losing "only" 13.3% vs. 14.22% for its category.
ISTM the question is whether one is willing to hold higher risk categories over a long term for a payoff, recognizing that long term is not one or three years but more likely five or even ten years. If that's too long to stay pat, then intermediate term core bond bonds would seem a better fit.
FWIW, I haven't reacted with changes to my portfolio. The only changes I'm contemplating are lateral moves (not category changes) that I've been looking into for years. I just have a little more data to work with now.