Overviews are probably the worst aspect of the new modern plex scanner. As you say, they are all over the place and lots of times are a right mess and outside of us editing the summary directly in plex itself we have no real control over it 
Anyhow, if you have any free votes consider placing one [Feature Request] Ability to specify Metadata from a single source (IMDB, TMDB or TVDB). Will it make any difference, probably not but we can always hope.
