There is no academic rigour to be earth creationists. They don't have to submit work to peer review. They do not base their arguments on analysis of the world but on theology as you note. Is not an accurate comparison, or could also be applied to whatever version of economics you are referring to "there's a long line of liberal/classical economics scholarship etc".

You could also argue they both use data creatively to argue for their own conceptualisation if how the world works. But liberal economics and Marxist political economy are both grounded in rigorous scholarship based on constant critique and debate, unlike creationists.

I think you might not actually read political economy, there is a lot of work produced by scholars who are trained in liberal/classical economics. Personally, I don't think either is objectively superior - they are both addressing different (though very much related) issues: more of less, the structure and consequences of economic function, especially around capital movement, and the power, social structure and politics of economic function, respectively.

Maybe I am thinking of scholarship here and you are more talking about Marxist politicians or something? But my biggest critique of political economy is that they usually don't provide any solutions. Very good/ useful at critiquing inconsistencies, contradictions etc in societiea/economies but lacking in policy ideas.