>Interest rates have been dropped into the ground, and it hasn't increased investment(growth). We have the highest savings in the history of capitalism and the lowest level of investment.

Savings _rates_ in the US are actually low by historical standards: https://tradingeconomics.com/united-states/personal-savings (click the 'MAX' timespan toggle). Low interest rates discourage savings and encourage borrowing. One of the fundamentals of economics is that all other things being equal, in the long term savings is needed for growth: if we consume everything we produce, then nothing remains to be invested, so productivity won't increase. If we save more, then we have more to invest, and this greater investment will increase productivity more.

The key thing to note here is that it is investment of forgone consumption that produces value (at a simple level, compare saving some wheat seeds to plant next season vs eating them all as flour). Lowering interest rates, printing money and similar things don't achieve this: they can create _money_, but not necessarily value. What they can do is increase demand, to address temporary shortfalls in demand, which under a popular form of economic reasoning will produce more growth than letting demand slump. That demand-boosting approach is however meant to be used as an immediate solution to a temporary slump, not an ongoing thing, as few economists deny a long term positive relationship between savings rates and growth.

There've actually been attempts to model what the ideal savings rate would be: https://en.wikipedia.org/wiki/Golden_Rule_savings_rate. Such models seem to have little influence on interest rate policy, however.