Games aren't actually hard to make, now that there's a completed Pokémon starter kit for RMXP. It has all the 3rd gen Pokémon, moves, abilities and items coded already, as well as parts of 4th gen.
What hackers call 'scripting' is much easier to do with RMXP, and has more features which can't be done in hacks. What game developers call 'scripting' is impossible with ROM hacks.
Here's the main advantages of each method, assuming you use the starter kit:
ROM Hacking
-Attack animations.
-Already have a region to start with.
-Ability to play on GBA/DS using flash card.
-Don't have to code advanced features such as contests.
-Tools are free (RMXP costs $60).
Game Dev
-Not restricted to editing pre-made things.
-No 25 new Pokémon limit.
-Less limitations overall.
-Much easier to insert Pokémon, sprites etc.
-No need to index sprites.
-'Scripting' is much easier.
-Can add new effects for moves, items etc.
-More control over some things.
-Most importantly, you can edit the actual game engine, for example, you can change the menu system or the screen resolution.
-However, the scripting language needed for more advanced features is quite hard to learn, but when you do, you can do nearly anything.
It really depends on what you want to achieve. Try looking around the hacks and games to see what's possible with each method. If I tried ROM hacking, it would feel really limited compared to what you can do with RMXP.
And asking in Game Development is going to be a bit biased. Try asking the same thing in ROM Hacking.
EDIT: You could always try both, and see which you prefer.