The one advantage that simple single/multi select fields have is that for the most users, they just show up as drop-downs which are easy to use and understand. Relations to entities (one-to-many or many-to-many) have a much more sophisticated rendering and can sometimes confuse users, especially the ability to drill-down into entities:
Things are even worse when it comes to multi-select relations:
It would be amazing if a “Display as” option was provided whereby you could basically tell fibery to treat/render some relation fields as single/multi select fields.