Map textures, resolution and details definitely seem to affect performance.
I absolutely love the Imperator map. But also, people should know that when it comes to actual scale Imperator map is much smaller in comparison to giant world map of Vicky3 (which is actually pretty decent looking, and has to exist on top of a massive performance-hogging database engine) and the similarly global map of EU5. Even CK3 is about to increase in size by another 1/3 soon, and it already has to manage active complex characters at every corner of the map.
For a modded example of the map texture issue - the CK3 AGOT team made their map really high quality with all the little details in Westeros + currently western Essos (and with a GIGANTIC number of individual counties and baronies)... and while it looks amazing the modded game struggles to run really hard on decent PCs and laptops from just a few years ago (even with a good SSD). It would straight up turn into a slideshow at times. Then came the launch of a couple submods that 'simplify' the map textures and replace them with slightly low-res ones... and guess what, the game immediately starts running normally at a good pace.
Imperator was the last Paradox game to be able to run smoothly on older/less expensive machines for some reason. I don't know if it is because the game lacks a LOT of features and they refused to add any before abandoning it, which unintentionally run so smoothly. The exact same scenario happened 10-15 years ago with more primitive Paradox games like EU-Rome or Sengoku or MotE - they all ran much faster than much more feature-heavy games like EU3, CK2 and EU4. Or maybe it is the result of Imperator's much smaller scale and map (you can see noticeably shrinking performance when mods like Terra Indomita which expand the map eastwards across Asia). Or if it is because of some newer version of Clausewitz engine. But either way, Imperator pulled it off with its excellent map, not every game can.
I think most people don't mind a 'simplified' looking map as long as it is still looks good enough. V3 did it successfully, CK3 requires mods to look great but isn't bad on its own. Looks like EU5 will be the same and that is not a bad thing IMO. I don't mind giving a pass to an Imperator-tier 10/10 hyperrealistic satellite map as long as the game still looks good and doesn't kill performance on moderate PCs.