Typically, the expectations from an SDK game and a hack vary. For example, since hackers already have fully functioning battle/menu systems, typically people judge a hack based on its content - story, tiles, balance, etc. With this said, though, hacks don't necessarily have to be entirely "new games". There are many hacks which just make minor changes to the existing games, like changing wild Pokémon and making trainers harder.
Part of the challenge of making a starter kit game, though, is emulating these features and creating a world from the ground up. I'd say that hacking is more about improving and/or adding to what's already there, while game development is more about innovation.
Both platforms have their limitations, though. Hacking ROMs, while free and convenient, is treading on dangerous legal grounds. Making games in RMXP gives you more options at the cost of accessibility.
