I do agree with Draco, up to some point... Much easier work for the developers, I think that will be appreciated.
However, that is also exactly the reason new starter types should be implemented. Make the game more difficult if you start with a simple pokemon at the beginning of the game... What if you started as a bug catcher with a weedle? What if you started with a level 10 magikarp? A tyrogue*? Alternate starting scenarios for enchanced difficulty might actually be fun.
The scenarios would be "preselected" off course. An appropriate rival pokemon would be selected for each starting pokemon, no randomness...
*Tyrogue is indeed a fighting pokemon, but his moveset is actually very limited unless it evolves, had to check in generation 4 pokedex to make sure... It only knows tackle, helping hand and fake out till 20... Challenge accepted?