Aperture vs Photos, no hierarchical Keywords?

Am in the process of importing my image libraries from Aperture (3.6) to Photos.

Keywords are very important for my workflow etc. I have long had a carefully-organized hierarchical Keyword structure in Aperture. For instance, only under such 'Head' categories as 'Orientation' do I add 'portrait', 'landscape'; similarly, I've put the keywords '35mm' and 'digital' in 'Image Type' etc.

Am I right that Photos does not/cannot preserve this - and that such 'Heads' ('Orientation', 'Image Type') will come across during import from Aperture as actual Keywords themselves?

If so, is there any way around this; does anyone have any other ideas/advice, please?

TIA!