remember that a few videos performing bad does not mean your whole channel or upcoming videos will be negatively effected forever. NO!!
that is not the case.
even if ur channel performed poorly with low retention views for a while and later on u push out videos that constantly have high retention and get good engagement, then your channel and upcoming videos can be revived and your stats will gradually improve.
same goes with ads. if you get low rentention views from ads when u initially purchased it, that would mean youtube may not push out your videos much due to poor performance, but that doesent mean your channel is in any sort of "blacklist" forever, such that it can never get pushed out by yt ever again.
in the future if you buy ads again but if your content is good such that it keeps retention, then yes yt will push out the video.
the main thing you need to remember is , people that experience negative effects by buying ads are those people whose content is not good even tho they think it is.
when you have great content ad views will most likely give you very good retention. also if you can try to use more of discovery ads then skippable video ads as people so often tend to skip these ads. discovery ads is placed on the sidebar and the people will only click it if they are interested in the thumbnail and what it is about.
also remember the final point that all big music labels,indie artists, vevo music stars etc, a large amount of their budget will spent for a mix of youtube ad views, maybe some smm panel views, website embed views, pop up ad views etc.
these people usually promote with large amounts of ad views, yet when u open yt home page u can often see these videos recommended coz from the ad views itself the retention of these music videos would be quite high.
also im referring here to just the indie artists that purchased views that get on your recommendations.
usually the big artists like bieber,arianna grande etc such people have big influence and usually their videos would get boosted by YT itself.