Variable default_bundle in migration? Field collection to varying paragraph types
Don't use the default_bundle at all, instead set the bundle type like other field values in the process section:

process:    
  temp_bundle_type:
    plugin: static_map
    source: field_list_item_type
    map:            
      card: card
      header: header
    default_value: card 
  type: '@temp_bundle_type'