I don't know what his point is. There is no absolute level of low or high interest rates.

Interest rates merely balance the supply and demand of/for labor.

Growth usually happens when there is high demand for labor and that means interest rates are high during periods of growth. When you think about it, interest is just the risk adjusted yield of a labor saving investment plus minus bank fees and profit share of the borrower. That means the existence of high yielding investments is what drives interest rates up as lots of borrowers got to the bank and present their fantastic business ideas and the bank picks the highest yielding ones.

Well, I also have to say something. Growth didn't really stop with lower interest rates. The economy is much bigger than 30 years ago.

Also about negative interest rates, it's a fallacy to think they are supposed to stimulate borrowing. They are supposed to balance people's desire to be in debt with people's desire to hold onto credit (equivalent to demand/supply of labor). That means negative interest rates exist as a disincentive to save money because nobody wants to borrow money.

Richard Werner is a bit nutty but his work does have value. He takes a heavily heterodox position on interest rates, some of this is him being misleading in order to be controversial. But his points about the impact of interest rates on bank profits are very trenchant (and btw, the reason why he is a bit nutty is because his professional experience was Japan in the late 80s/90s, that scenario tested all the assumptions about macro and found a lot of them were false, his book Princes of the Yen is good...although, again, very heterodox).