That graph basically makes me think there is no "normal" and no trend, it appears to just jump all over the place, widely, continuously. i don't know if that's right, but that's my reaction to that graph!
You're right. The data shows "across successive monetary and fiscal regimes, and a variety of asset classes, real interest rates have not been 'stable', and that since the major monetary upheavals of the late middle ages, a trend decline between 0.6-1.8bps p.a. has prevailed. A consistent increase in real negative-yielding rates in advanced economies over the same horizon is identified, despite important temporary reversals such as the 17th Century Crisis. Against their long-term context, currently depressed sovereign real rates are in fact converging 'back to historical trend' – a trend that makes narratives about a “secular stagnation” environment entirely misleading, and suggests that – irrespective of particular monetary and fiscal responses – real rates could soon enter permanently negative territory" [1].
Basically, over the very long run, real rates go down 0.6 to 1.8 basis points (1/100th of a percentage point) each year, and tend to be low. We've witnessed a few centuries of extraordinary growth, which mandated resource prioritization, which kept rates high. TL; DR Anyone talking about where rates "should" be based on looking at charts is often talking tripe.
[1] https://economics.rutgers.edu/downloads-hidden-menu/news-and....