Some pokes can't learn moves in bulbapedia but have other skills in PA logic?
The logic is that we do our best to follow Bulbapedia and to do pokemons' movesets by there, but if in any case we think any pokemon needs more AoE moves, stuns, or even melees, we will have to find another way to improve the pokemon, but I assure you Bulbapedia is always our first option to do any kind of moveset.
Lemme give you an example:
Ambipom in Bulbapedia:
That's Ambipom in PA:
so my question for you is simple. Would you be able to level an Ambipom if we have done its moveset based only in bulbapedia's moveset, and giving you a pokemon with only Fury Swipes as AoE?
If in any case you find something different from bulbapedia, it means it was needed, not because we wanted. There is not needed to add Iron Defense to Steelix cuz:
1º - It doesn't learn Iron Defense.
2º - It learns another move with the same effect, which adds the same amount of defense.
3º - It let us save one more place to any other sprite, which probably will be used by a most useful one.
I don't want to be rude but, will I need to explain you the same thing for the 3rd time? '-'
Hope you get the logic now.