Addressing those "grievances" hasn't worked out too well for Russia. They complained about Ukraine moving in the general direction of NATO membership, and got Sweden and Finland as actual new members of NATO. Finland has a longer Russian border than Ukraine, and Sweden has a regional navy that pretty much controls the Baltic Sea. Both countries were pretty firmly neutral before the war.
Because for all of Russia's apocalyptic rhetoric about the dire consequences of NATO membership on their borders, they've done nothing significant about Finland and Sweden actually becoming NATO members while stepping up their military spending. By comparison, a little political noise about Ukraine maybe joining NATO someday is much less of a provocation, which makes it seem unlikely to have been Russia's actual reason for invasion. And from any reasonable ethical perspective it's certainly not a legitimate one.
and that has what, exactly, to do with the legitimacy of said grievances?