I work in ad tech, and indeed some areas and experiences are less-than-optimal, especially in RTB. Unless the site owner is selling highly-custom take-overs, skins or other non-standard formats, ad interference with site content and layout is almost entirely eliminated via the use of iframes.
I consider iframes to be basically the most egregious ad insert.
Why? It is safer, doesn't block loading of main page assets and causes way less breakage when things go wrong.