Just a couple of years ago, having frequent meetings and exchanging (weekly) emails with the ad network representatives, without a doubt had a significant impact on the performance of the network. I remember going back and forth between the ad networks to negotiate for the higher ecpm in exchange for the first impression, with a lot of manual work and things to keep track of.
With more and more self-service solutions allowing publishers to self-manage, creating new placements, setting ecpm floors etc, luckily has made running day-to-day ad ops easier, at least for a smaller sized company where we don't have a team dedicated to doing ad ops full-time. Bidding makes it even easier, even though it still takes time to optimize waterfalls in a hybrid solution.
With frequent restructuring in the ad network's organizations, and of course the covid situation canceling all on-site conferences where you would normally network and meet people, I find maintaining the client/partner relationships with the ad networks more challenging than before. But at the same time, maybe it is sufficient to have someone to reach out to for advice every now and then, and just let the mediation do its work. It is for sure less time-consuming.