FDR did not have to do any maneuvering whatsoever to get his 4 terms - Grant had already run for a 3rd before him, as had Teddy Roosevelt. There was no rule against it an the people wanted him in power, so he stayed in power. Similarly, GWB didn't run for a third term, regardless of what he "could have" done. Neither of your examples are very strong here.
There has never been an anarchist "experiment" capable of sufficient coordination to produce modern (for its time) medicine, or the agricultural technology needed to feed current populations, or housing and infrastructure fitting of modern standards, and so on for many other goods and services we consider necessary to life today. Anarchism has almost sort of worked for a handful of small-scale, already-impovershed revolutionary/resistance groups, who can rely heavily on pre-existing infrastructure and some trade with capitalist or state communist industries, but there is little evidence to suggest it would be able to work on a meaningful scale. It also has a tendency (such as in Spain) to be co-opted by wannabe dictators anyway who simply establish oppresive state communist regimes regardless.
Soviet-style command economies are already notorious for being unable to match capitalist economies in terms of efficiency, due to the simple fact that it's far easier to use natural pricing (maybe with some interventionism) to reach equilibrium than equations and top-down production quotas. You can make an argument this could change with help from modern data science and machine learning but that's beside the point. With anarchism, you are taking all of the issues of soviet-style economies and making them even worse in that now each individual commune is responsible for coordinating with every other one it relies on. Even if you don't prevent natural currency systems from developing you still lose massive amounts of efficiency and still end up with inequality (due to resource, skill, etc. distributions being inherently different), though this time maybe you get lucky and the ienquality is between communes as opposed to being within them, between classes.
Also, there are practically no cases of lasting nonviolent anarchist revolutions. The haves tend to really not like giving up belongings and lifestyles to the have-nots when forced to. That's obviously not an argument against anarchism, though.
If the size of the flung-off objects is proportional to the size of the asteroid that may be the case, but it's also possible it's mainly proportional to the force of the deflecting impact. Regardless between a potential extinction-level impact and hundreds, even thousands, of smaller, "Hiroshima-sized" impacts, the latter would still be massively preferable. Statistically the majority would hit the ocean and do little to nothing as well.