I was one of those who stumped for something like this and detailed the issue (and related ones) back in the comprehensive community issues thread. Yes, a de jure kingdom title in the area is ahistorical but needed for the gameplay mechanics to work correctly. The AI uses the de jure map for target weights/priorities and such. This is also why the hypothetical/fictional empires are needed. The AI, especially pagans (with the become king ambition), cannot function properly without it (unless you make a major overhaul of the scripting).
In my personal mod I play around with the de jure borders a bit (mostly shifting kingdoms from the ERE or Arabia to their appropriate regional neighbors to encourage rational expansion) and return the inflated catholic Iberian realms to what they really were: petty kingdoms (independent duke tier -game mechanics wise), and the "Empire of Hispania" was likewise a self inflated kingdom (-merge it with Francia with localizations for Spanish/Andalusian/etc cultures). I then make the fictional titles uncreateable for the AI (ai = no) so they get the encouragement to move in a direction but not the mechanical boost of the inflated title unless they really earn it with a custom title. I'm experimenting with making most be tribal titles also (tribal = yes) so they self delete if equal or higher titles are acquired. (I'm unsure if this last will work correctly since I haven't noticed it used for several patches and DLC updates... but option is still showing as existing -with the rebels at least- so I'm trying it. It'd be nice to have this work for a lot of the Baltic/Slavic/Russian/steppe duchies also. This is my solution to the France creates Aquitaine/Burgundy/etc issue.) I also try to consolidate the 1-2 county de jure duchies into 3+ county ducal regions, and sometimes dividing a 3 county duchy and distributing it to it's neighbors (making the smaller title titular instead if it should exist at all, only keeping it de jure if there is a damn good reason for it -eg: Venice).
The goal being to encourage titular custom kingdoms and empires instead (who can still assimilate through drift) and to cut back on the glut of (permanent/persistent) kingdoms/etc auto-created by EG succession. If I were a better modder I would a simply remove the Sampi provinces entirely (and Iceland to boot) and make them like Siberia/Sahara to fix Scandinavia (people live there but politically it's empty/useless until well outside the time-frame). I like CKII+ and HIP but some of the design choices are counter to what I'd hope for (I don't like removing player agency and some of the map changes, but having big titles be event created only is great) and they're often well behind the patches (because how long it takes to update such massive mods).