Meowth around the world are fond of shiny metal objects – perhaps even as fond as humans are – and the steel-type breeds native to Northern Europe are no exception. Once these Meowth evolve into Perrserker, this fondness evolves with them into a sort of obsession tinged with wanderlust. But coins were hard to come by in a remote Old Norse village, and trying to rob a Jarl was highly likely to lead to their capture. (A likelihood increased by Perrserker's habit of stopping everything to play with coins, instead of first stealing them away.)
Perrserker often participated in viking expeditions, some as wild volunteers, others as members of the Jarl's own retinue. They served as lookouts when sailing at night, and once on shore their steely spirit inspired their armored comrades, pushing them on to ever greater feats of strength and valor. An unarmed commoner can struggle to take down even a Meowth, and even hastily assembled groups of militiamen and pokemon struggled with their evolution. Flanking did little against a foe with claws on one side and daggers on the other, and medieval pokedexes testify to even knights' frustration with Perrserker; they describe the species' entire body as made of armor, leaving enemies clueless on where to strike.
It should not be surprising that Perrserker replaced Persian in Galar; the puzzling thing is that the same did not also happen in Kalos. Perhaps it was that the greater wealth of Kalos' kings rendered Perrserker too willing to leave fights in search of treasure, or perhaps the military use of speedy fire pokemon such as Talonflame and Pyroar gave Perrserker a local reputation for weakness. But Galarians have not regretted Perrserker's absence from their ancient rival; if anything, it helped them embrace this Viking Age immigrant as one of their own.