Drawing is certainly NOT a key foundation skill for learning design (at least if we're talking about designing websites and user interfaces). Certainly not on the same level as typography, for example.
I think a good equivalent would be math and programming. Being good at math can certainly help with some things, but if someone asked me how to become a Rails developer I would not suggest they start by learning math.
Learning to observe critically certainly _is_ a foundational skill in any kind of visual design. Observational drawing is probably the best way to develop that skill. Do it or don't, the choice is yours.
Anyone wanting to learn programming should know algebra, set theory and a bit (!) of logic. You can pick these up as you go along, it's not magic, and often that's the way the world works. But I wouldn't recommend that as a preferred choice. When you just pick it up, there are holes in your toolset, holes that you might not even know about. And worse, holes that make you defensive about your skills.
And not strictly apropos to this branch of the conversation, I would recommend anyone interested in any kind of visual design should study geometry. Good old high school plane geometry is a good place to start. I can also recommend descriptive geometry, particularly the courses aimed at engineers and architects. Anyone that gets into designing type, and with type, who lacks this knowledge has a very real handicap.
The advantages these disciplines offer the designer or visual artists are indescribable to those who lack them. Either take my word for that or ignore it.
Certainly people have done well without them. But that's a limitation that has been overcome rather than advantage.
And of course a true genius in any field can do what ever works for them. I never managed to arrange to be a genius so I have always had to limp along with what I could learn.
I think a good equivalent would be math and programming. Being good at math can certainly help with some things, but if someone asked me how to become a Rails developer I would not suggest they start by learning math.