Most political cartoons in newspapers are left-wing and most and most memes on the internet, at any rate political memes are right-wing.
The cartoons seem more likely to come off as propaganda because they are caricatures trying to distort reality and they are not funny. They are unconvincing for the very same reason that American caricatures of the Japanese and Nazi caricatures of the Jews are unconvincing. They try to create an augmented version of reality but when the real thing is placed next to the augmented version it becomes just a caricature that exists to push an agenda and couldn’t exist otherwise even in the eyes of those who believe in the rhetoric.
Memes, on the other hand, are purely fantastic. Even from the time that the left used to clearly have the upper hand on the internet around 2008 to early 2013 there isn’t much in the way of image based humour from that period except some anti-Christian memes by some atheists but nothing as fantastical as pepe the frog. Of course I am aware that much that goes on the internet is inconsequentional and that that is made further so by the segregation of different ideological groups into different corners of the internet. There are some who have tried to change this (i.e. to reach out to the normies) but it still is an interesting phenomenon that such ‘subversive’, ‘reactionary’, ‘problematic’, ‘counter-culture’, ‘irony’ what you will call them will depend on your political affiliations, at any rate, these ideas are not mainstream or socially acceptable can be made socially appealing through humour.
I am not convinced by the ‘it’s just a meme’ excuse at all, that they are doing this just for shits and giggles and to say the things that most would not dare to say. I think many of them believe in what they profess. It would be just as well to claim that the great composers and poets faked their faith in God.