Originally ad networks were something you rendered out on server side hitting their APIs from the server, and in some cases dns via subdomain. Content hosts were more careful of the content of the ads because it hits their main host ranking.
First party / server side ads are actually preferred if you have to choose as you can limit the ads server side and rogue ads can be dealt with.
Ad networks from the late 90s to early 2000s were this way. Once popup ads took off they started making ad networks client side to not impact rendering on the server and ads could show progressively when inlined into the layout/script.
Today the ads/trackers are almost all client side as it is easier to integrate as more of a widget and less resources used on the server. The ad networks and trackers of today want to own all the data and not share it with content providers, plus being client-side it makes it easy to link data without the need for integration in each endpoint backend just the third party endpoints. Additionally third party ad networks may not trust that page views are organic with the api calls being implemented first-party server side, so they went client-side where they can validate actual page renders and lots of other time/click based metrics.
Ultimately sponsor ads that show up on sites/blogs/portals are usually first party server-side ads still. So as long as there aren't rogue ad networks on the server side or via DNS/subdomain then it may improve ads overall. Since first party ads are server side, unless routed via DNS to the ad network, at least the content provider incurs some cost from hosting it at least in bandwidth. If it is a subdomain that goes to an ad network that is full of dark patterns, that is not so great but it will still impact the host reputation in ranking.
Right now ads are a mess for a few reasons: so much tracking, taking up screen real estate and the marketing team pushing people to subscribe making the free content experience painful. Email/subscribe and ad popups are more prevalent than the behind the browser popups in the early days, very bad experiences.
I sometimes think the days of server side/first party ads and popups from the early internet are preferable to today's inline ads with videos that follow you down and autoplay nightmares all over the page with dozens of trackers and networks all in one. At least first party server side ads that are served up from a backend API hit to a third party or sponsors doesn't cause excessive connections, it also puts an upper limit on the amount of ads that can be shown before it hits costs of hosting and rogue ad networks impact the url reputation so the content hoster may be more of a curating check on ad quality.