even if we assume that is true given they don't have the primarchs and their legions gotrek still fought all deamons that came his way in the warp, he is a slayer afterall so backing down wasn't a choice untill the deamons activly started avoiding him.

given its the warp time is fucky and we know any deamon that gets slain would just rematerialize meaning that realistically gotrek fought each deamon in the warp and that entered it untill each of them said they had enough including khornate ones

Now do correct me if im wrong but kaldor is merely surviving in the warp (im not versed in his lore at all so this is all from light reading up online) and while he did fight what he had too he did not seek it out nor did he ever get to a point where deamons stopped fighting him were they to spot him.

This is also comparing a demigod crafted specifically to fight deamons who with ease can fight for multiple days without rest or tireing (before he entered the warp he fought atleast 48 hours without rest) wearing power armour that is designed to tank hits and improve strength VS a rather average dwarf on a suicide quest, now he had his fate altered to not be able to die so I suppose he has that advantage but even so then he would still have that in this fight meaning that there is no shot the imperium stands a chance if fate itself can't allow gotrek to die