Talking about theory as a single subdomain of CS doesn’t really make sense anymore. It’s a wide and varied field. I have friends who work mainly in automata and

Talking about theory as a single subdomain of CS doesn’t really make sense anymore. It’s a wide and varied field. I have friends who work mainly in automata and complexity and have worked with people focused exclusively on a single class of algorithms. They’re remarkably different in difficulty. My friend in complexity is clearly a mathematician. My friend who is an expert in random algorithms is doing a lot more throwing darts at a dartboard with enough theory chops to make his papers interesting. I studied CS theory and modeling in university and my degree was effectively a math degree. Without the math and analysis piece I don’t think the theory ever would’ve been intuitive.