Actually it is a mixture of Marketing and (html) programming. That is if you look at pure
SEO (getting higher positions). Webdesign comes in to play when you want those visitors also to do something on the site. So in the broader view of
SEO, it's a mixture of Marketing, Programming and Web Design.
Now there is a problem here.
The problem is that there hardly exist any people that are good at AND web design AND marketing AND Programming. 2 out of 3 is the best that you can get and still of those very few actually exist. Generally people are good at just one thing.
But these people have the same problem as you have. In order to do good
SEO you need all 3 skills.
Most
SEO's are technical people because HTML knowledge requires learning HTML language. You can not have a feel for it and just know how to program HTML. Marketing and webdesign are less abstract and you could do something without having to learn it first. Wether or not that will be any good is another thing, but you can at least do something. Without HTML knowledge you can't do anything.
This pretty much also explains why comunications between these different fields is so bad. These fields are so different from each other that the focus of one is the thorn in the eye of the others.
You said you´re a student so I'll assume you don't have the experience yet that shows that different departments are really good at not understanding each other. That has nothing to do with comunications, as is often suggested. It's just that priorities for each department are different. It is a very difficult job to get everybody's priorities synchronized, especially in bigger companies and between different companies that have to work together.
The really good
SEO is capable of getting priorities synchronized (even if it's just for a short while). Inside a bigger company, consider this person a project manager with the knowledge but not being the one that actually does all the work. (S)He needs to be responsible, develop strategies together with the departments, but specifically not be the person that's doing the actual work.
It would be best to have this person not work in any of the departments but to have her/him report straight to higher management. That will take out the competition factor so people are more willing to agree.