Are Shadow Pokémon more or less powerful?

Question

Note: This lore comes from Pokémon Go but I'm asking the question here instead of Arqade Stack Exchange because I specifically want to know about the lore.

This says that the Shadow Effect that team Rocket puts on Pokémon makes them more powerful:

But once you free a Pokémon from team Rocket, you can purify them. According to this description, purifying the Pokémon makes it more powerful too:

This seems like a contradiction because purifying seems to imply that you're returning Pokémon to the way that they used to be.

Unless a Pokémon is ultimately better off after being turned into a Shadow version and then purified than if simply nothing had been done to it (which would be a counter-productive narrative since then we should actively try to turn Pokémon into Shadow versions so that we can purify them).

Answer 1

Shadow Pokémon originate from Pokémon Colosseum and Pokémon XD: Gale of Darkness, where they are described as Pokémon that have had their emotions removed or inhibited through scientific means. This process doesn't inherently make them stronger, but it does make them more aggressive.

Pokémon fights are generally treated as being friendly, playful affairs, with the Pokémon holding back their true strengths so as to avoid injuring each other or causing huge collateral damage. Shadow Pokémon (and other Pokémon with inhibited emotions, such as the clones in Pokémon: The First Movie) do not hold back in the same way. So their power level is the same as a regular Pokémon, but they are willing to use more of that power, if that makes sense.

In Colosseum and XD, this manifests in the form of "Shadow Moves", which cannot be resisted by non-Shadow Pokémon in Colosseum, and are super-effective against non-Shadow Pokémon in XD. In Pokémon GO, this manifests in a 20% power boost to all the Shadow Pokémon's moves. In both cases, a Shadow Pokémon is indeed more powerful than a regular Pokémon with the same level and IVs.

Purifying a Shadow Pokémon in GO erases that power boost, but slightly raises the Pokémon's IVs and substantially raises its level. I'm unsure of the lore reasons behind this. Whether the IV boost is better or worse than the attack boost - i.e., whether a Pokémon is stronger or weaker after it's been Purified - is a matter of opinion.