Thank you for the insight @Canapin.
Thank you for the specification about basically returning only topics. Completely missed that 
As a workaround, when the search result return the actual results, it builds the URL, do you reckon we could have a component/plugin that simply add a style="display:none" to the ones that follow the URL format that specify a post and vice-versa for topics.
In the case of a plugin, somewhere in the search results there must be a function that determine “this is a first reply” or “this is not a first reply”. Maybe it would be possible to intercept that and skip it from being added to the array of results given a specifically added new filter?
If you know which file has that controller/model, can you link it here so I can give it a look as well? 