There are about 5 or 6 absolute monarchies left in the world. I can't see there's any real risk of romanticising monarchy by having fictional examples of monarchies led by people with vast superhuman powers in the Marvel Universe. No one's going to think, well, OK, Saudi Arabia's an amazingly well governed country, because they read a story about Black Bolt shouting at Thanos.
Of course, it is fair to say that the Marvel Universe generally suffers from the most appalling governance, although perhaps that is scarcely surprising in a Universe with alien invasions every five minutes, killer clouds, reality changing super Nazis, and actual Gods knocking around the place to ridicule the institutions of mainstream religion.
That said, Hickman's Avengers/Illuminati runs would have been very different without the monarchs - the whole conceit was that Black Bolt, Black Panther, and Namor made their decisions regarding the incursions as Kings - not as heroes. If we are stripping the monarchies out of the Marvel Universe, lets hope that their replacements offer as many storytelling possibilities.
Of course, I understand the current Black Panther run is regarded with universal acclaim and affection by the Black Panther fanbase, so no doubt they're all delighted by the move to Wakanda democracy and the many interesting stories it will engender