Feynman is an outlier, a very rare talent that could handle very complex maths and also communicate these concepts in an approachable, charming, and laid-back style. This is an in-born talent and also a skill that can be taught. But communicating complex systems is a separate proficiency from understanding those systems.

The main issue when explaining concepts (especially maths concepts) is switching from one formal context to another, deciding what details to omit, and determining what rules in both contexts should be treated as analogous.

Think of a translator. He/she/it needs proficiency in two languages to do a proper translation. Lacking a second language precludes translation. But it doesn't affect mastery of your native tongue.