the problem with any sort of "who is the strongest" argument, is that it never really gets answered. GW rarely definitely states who is the most powerful. even when two big characters fight its usually resolved some other way. One guy is winning the duel, but his army loses. One guy is losing the duel, but his opponent is pulled away by the acts of someone else. lots of stuff like that.
also in the lore, magic can be used in duels, so a mage can theoretically whoop up a really good melee character, but it isn't a given.
and you also end up with a lot of Warhammer Lore isn't transitive. Just because character X beat character Y doesn't mean character X would beat the guys that Character Y did.
and a lot of it also comes down to various magic items, that the individual who is using them may not have created. So can you really say the user is THAT powerful?
Going back to Gotrek, he is the strongest Dwarf, could defeat any other Dwarf in one on one. But its got a lot to do with his axe. which is one of their god's literal axe. he was still powerful without it, and how he got it was pretty crazy (he walks into the chaos realm), but he is definitely much stronger with it. and then the power of the axe has also made Felix stronger, and apparently Felix & Gotrek's fates are tied together now, so they are also even stronger when together, than when separated. and basically they can't die if together unless both are taken out. so how does that team count?
Several other characters also have friends/pets/allies they always travel with that make them stronger. Skarsnik & Gobbla, Skarsnik isn't a great fighter, but Gobbla is. The most powerful Skaven Thanquol, and its a crime he still isn't in the game yet, is the strongest Grey Seer, but he has a upgraded undead Rat Ogre as a companion. Imrik of the High Elves is considered one of the best, but if you put him on his dragon, he is clearly the best, and that dragon taming is one of his powers, so its difficult to separate. Kroq-Gar is the oldest Lizardman around, and probably the most powerful non-slann, who has solo'd multiple greater daemons over time, but he also gets a Carnosaur, and some insane magic items.
and then you have some relatively minor characters who are hard counters to various OP characters. Nagash is at worst the second strongest character in the setting, but there is a random Tomb King that has found ways to defeat him multiple times in the past. There is a random Empire champion who has defeated both Archaon and Grimgor, but loses to a non-name chaos character. Grimgor has other fights that he clearly wins, but leaves the enemy alive because it was a good fight, and those characters typically go on to get stronger, or go find a magic item. The Chameleon Skink Oxyotl is a hard counter to any daemon, including Kairos Fateweaver being straight up scared of him, and daemons don't feel fear.
and then you have some characters who are just kinda cursed. Like they should/could be top tier, but just quiet aren't for various reasons.
Belakor should be the strongest daemon, so powerful he almost became a Chaos God, but the other chaos gods teamed up so that couldn't happen. Thanquol, the skaven grey seer, is theoretically powerful enough to cast a spell that would table the all of humanity on its own, but Gotrek & Felix always jack up his plan. Malekith is the second oldest elf, besides his mom, who is insanely talented, powerful mage, rides a dragon; but can't get over his father's curse.
and then you get the miscaleanous characters that GW doesn't go into, who would really be more powerful than they appear in any game. The Green Knight is rumored to have killed an underwater dragon nation by himself, and visited their god's realm. The White Dwarf Grombrindal is the oldest and maybe most powerful Dwarf, who might have been banging their god Valaya from way back from before chaos was a thing and a friend and compatriot to their other gods, but the lore isn't even clear on if he actually exists now or ever really existed, yet alone what he actually can do/has. none of the Cathayan characters existed on the table top, but in lore are actual demi-gods themselves, and they have fought more chaos than anyone. then you have the father of the Dragon-Ogre's who is the size of a mountain who is in perma-sleep, and lifting one of his fingers killed Archaon's strongest follower. There are also mountain sized dragons, a sky-titan who is also asleep that is the size of a mountain range.
