Authoring tools in general tend to add unnecessary tags, occasionally taking detours from widely adopted standards. That is not fundamentally wrong. Design Studio accepts any code. The rendering on the client side may produce few surprises.
Copy/paste between authoring tools and Design Studio is easy. The troubles are often hard to fix.
My suggestion is simple: start with a blank landing page template: Design Studio - New - New Landing Page Template
Save and approve without any changes. That will ensure the essential page definitions are in place.
Defining the landing page itself requires few minutes and attention to details. Start with Design Studio - New - New Landing Page. Select the template approved in the previous step.
Page meta tags are placed on Landing Page Actions (top right corner) - Edit Page Meta Tags - Custom Head HTML
Copy/paste the meta tags.
A HTML block page element would have the cascading style sheets (CSS, defined within style tags).
Another block for JavaScripts if present.
Landing page contents. Copy everything within the opening and closing body tags and add to anothet HTML block page element or click the HTML button in the toolbar to paste the HTML into the code area.
That process ensures the tracking works as intended, the contents are editable and simple to maintain.