>>54886644All English Pokémon media at the time of Gen 2 had Raikou pronounced correctly, from the pronunciation guide on the handbooks to Stadium 2 to the Johto Pokérap to even the anime itself.
The "Rai-koo" bullshit started with the dub for Legend of Thunder which happened in Gen 3 as part of the Chronicles compilation which had some of worst dubbing for Pokémon offered by 4Kids, they called Eusine "Eugene" in that dub for fuck's sake even though he was correctly called Eusine in the anime before that.
LoT, Battle Revolution, and at least one handbook from around then seemed to have been the only times that mistake was made since Pokédex 3D Pro and later anime with Raikou in it such as Generations has the correct pronunciation, but the damage was done if it affects Pokétubers to this day.