Why does Taranza just assume that King Dedede is the Hero of Dream Land without anything else to go off of? Just take one look at Sectonia. She's immensely powerful and, as we know, was once a just ruler before the Dimension Mirror more or less broke her sanity. Taranza assumes Dream Land's ruler to be its hero because their ruler was their hero.
Even though Taranza was wrong objectively, he ultimately ends up having made the correct choice in heroes, as both Dedede and Kirby save the People of the Sky from their corrupted queen.
Can double as Fridge Horror: Queen Sectonia is referred to and designed after a species of parasitic wasps - in the game, they are said to use their parasitic nature to subjugate others. Some of these wasps are known to specifically target spiders. Taranza is a spider/tarantula. Ever wondered why Taranza was so easily under her thumb?
Queen Sectonia's appearance is based on a wasp, namely a queen wasp. Normally, queen wasps live up to only twelve months, which basically equals a year. Can also double as Fridge Horror and Tear Jerker after you learn about Queen Sectonia's goal to become a goddess as well as her corruption into a tyrant through obsessive gazing into the Dimension Mirror.
Later in the game, we're told that Kirby was chosen specifically by the Dreamstalk to save Floralia. So why does both Kirby's house and Dedede's castle get lifted? Well, either a) the Dreamstalk knew Kirby needed motivation to go into Floralia, or b) both Kirby and Dedede would be fit for the task. Keep in mind, this game takes place relatively soon after Kirby and Dedede saved Popstar/the universe, and Dededetour shows that the King, as long as he has his hammer, is fully capable of saving Floralia by himself.
Why is the Dimension Mirror the force behind Sectonia? Because this is the first Kirby game where you travel between the background and foreground, or in the third Dimension!
Of course, in the last game where King Dedede was also playable, Waddle Dees will attack him like everyone else. Same with the playable Waddle Dee. But Kirby does do some mean things to them in this game, like put out a campfire or inhale some house in the vein of The Three Little Pigs.
This troper assumed that the Waddle Dees living in Sectonia's kingdom were outside of the rule of King Dedede.
In the intro, Kirby climbs around on some vines to get to King Dedede's castle. Despite the fact that he can fly. Then again, walking/climbing for Kirby is much faster than flying, so it makes sense he'd scramble up the vines if he was in a hurry.