Most of the people that say that the gameplay/design are similar to the Kirby series are forgetting that they're made by the same companies. Naturally, they'd wanna stick with what they're good at. My theory for why they used the style similar to the other Kirby games possibly is because Kirby is in it, so they decided to use the style similar to the Kirby games
On the subject of the Halberd vs the Great Fox, I don't really think we've seen the full extent of what the Halberd is capable of yet. Not really sure what else to say about that :D
I think the reason why there's more Kirby characters in Brawl is because there was only 1 character for the last 2 games from the Kirby series, so they brought in DDD and Metaspam to balance it out a little. Think about it, nearly every series either got a new character or kept the same number of characters: Earthbound got Lucas, Metroid got ZS Samus, Donkey Kong got Diddy Kong, Star Fox got Star Wolf, Fire Emblem stayed with 2 characters, Pokemon stayed with 4 characters, and so on
Also, Falco beat Bowser's *** pretty bad too
Just my 2 cents