There is no doubt that there was a need for the policies employed, and that authorities had to make use of all instruments at their disposal to prevent an even more severe downturn in the global economy and to prevent a collapse of the world financial system.
There is also no doubt that implementing some of these policies was an experiment of sorts, and central banks have always been ready to admit that this is new territory and exits from these non-conventional and non-standard measures could be complicated, because there is no blueprint to work from when it comes to the extent to which central bank balance sheets were put to use.