> The fact that on Earth the living beings eventually used ATP and RNA appears to have been determined in great part by chance, while the use of amino acids seems to have been much more deterministic.
It looks like on Earth the RNA was the initial replicant. RNA can be folded into complex shapes and can have catalytic properties in itself. Ribosomes that assemble proteins have RNA at the active site with proteins only providing structural framework.
That's why amino acids might not end up being so universal.
There is no contradiction: simple amino acids as a basic building block being coopted by replicating RNA to build more sophisticated structures.
You can conceive other than nuclear-acids based replicant, using the same ubiquitous amino-acids to build a protein life not using RNA/DNA but some other encoding structure.
The question is what is the chemically most likely 'other'? Also, what could be alternatives for ATP/sugars?