The player character exists as this weird, nebulous entity in the lore, and so actually figuring out how powerful a given character is might as well be impossible. This is because the story has now shifted from there being multiple ‘champions’ to a single PC in the eyes of the story, over time.
From Classic to arguably Cata, the player character was about the same power level as a Hero unit in the Warcraft games. Markedly stronger than most NPCs, but below the main characters, and many of the final bosses we fought were killed with help from major lore characters. So the NPCs we have as followers? They are roughly where the player character was in terms of power relative to everyone else, for the first six or so years of the game, with the assumption that there were many different ‘champions’ at all times.
The shift in story came with MoP, though there was a beginning to it in Cata. The story began going under the assumption that there was only one champion in the story, the singular Player Character. But the power levels remained more or less the same as before. That power creep and Main Character portrayal happened with WoD. Again we saw that the game treated the player as one of many champions, but per the story, the player character was the only one who survived and became the Commander of the Garrison, and got that shiny legendary ring. This put us above the other characters that would be considered equal to us in power a few xpacs before.
And it just kind of gains momentum from there. In Legion there is only one Archdruid, one High Priest, one Deathlord. Our followers are Hamuul Runetotem and Lady Liadrin. In BfA we have the Heart of Azeroth, and again in canon there is only one person with that artifact. The power creep is real, but so is the singling out of the PC as the only champion in lore.
Right now I would put the player character dead center between our followers and the major lore characters, with obvious variation for those characters’ power. Jaina doesn’t get forced to retreat by a full raid of Heart of Azeroth wielders, it’s a group of Horde champions on par with our followers in power, at most. Rast doesn’t get killed by a bunch of Alliance, each with their own Hearts, but by Genn Greymane and company.
It’s actually kind of weird, because the rest of the story doesn’t acknowledge the Heart of Azeroth at all, but at the same time that’s the reason our character is more powerful than, say, Shandris Feathermoon, and is able to shake off things that cripple various NPCs.