I think it's pretty easy to empirically find what's the right balance if we analyze history. In fact, I think most countries have already found that equilibrium

I think it's pretty easy to empirically find what's the right balance if we analyze history. In fact, I think most countries have already found that equilibrium, at least for government leaders. It seems to be 8-10 years at most. 20 years definitely feels like it's too long, even for super-appreciated leaders like Merkel, who I've seen make many bad/corrupt decisions lately, by propping up the coal industry, the polluting car industry, and so on. 20 years is just too long for any human to run a country. For Congress/Parliament members, perhaps a little longer would be reasonable, but probably no more than 20 years.