When I say "from the left", I'm specifically referring to "to the left of the Soviet Union".
There was a lot of active debate when the Bolsheviks took over in Russia on whether to support them or not because they were creating the first "communist project" at that scale. The disagreement was largely ideological and the criticism was eventually proven correct when the Soviet Union sided against the anarchists in Spain (as well as when they went after "Makhno's army" in Ukraine, as well as early on when they disbanded syndicalist groups and worker cooperatives, as well as later on when they went through rounds of ideological purges and so on). The most well-known discourse around this seems to be from German communists, where it was cut short by the killing of the Spartacus group.
When you say 1984 criticizes "political systems in practice" that is exactly right: the criticism of the Soviet Union wasn't that their stated goals were bad, in fact most of the left agreed on the ultimate goals. The criticism was that, like the pigs in the animal farm, by merely picking up the weapons of the oppressors they recreated the same oppressive power structures (i.e. systems). Anarchists on the other hand wanted to disband the power structures and replace it with one built from the ground up.
When you say "all systems of government" however, it's clear that you're likely unaware of anarchist theory: the problem is not government, the problem is the state. And it doesn't matter whether that state is a conservative or reactionary oligarchy, a liberal or Soviet bureaucracy, or an "anarchocapitalist" corporate board of capital owners: they all share the same structural problem of moving power from the subjects to the state and then using it against the subjects to legitimize the state's authority through violence.
In other words the point of Animal Farm isn't that oppression is inevitable but that switching out who's in charge won't make an oppressive system any less oppressive, it will just recreate the same oppression eventually.