I don't believe it is the same; I understood that they use the experiences gained by following several of the Aspect Paths to develop a well-rounded perspective on warfare, rather than the wisdom of those who were Autarchs before them (not directly - I am sure there are many texts and treatises on the subject). So far as I know they don't live in the Aspect Shrines. Most of all, they can leave the Path of the Autarch and do something else, and they elect to take the Path. So there wouldn't necessarily be a lot of spiritstones containing dead Autarchs, whereas every Exarch will die an Exarch and be so enshrined, unless he is the Young King. Becoming an Autarch is a choice, for an Exarch it is becoming stuck on the Path. That's what I've understood by it, anyway Is the Young King an Aspect Warrior now, or an Exarch? I seem to remember it changing edition by edition ... That is an amazing Warp Spider I'd always pictured the warp as dark in my mind, but there's no reason it should be and the bubbling, changing scenery makes sense.
I have also not heard anything about the autarch armor being anything else than a truly masterwork armor, fit for the field commander of the warhost. While an autarch may commune with his or her predecessors who reside in the Infinity Circuit, their mind is their own. This can make for a pretty cool picture, though.. an autarch holding council with ghosts and blank-faced wraithbone statues that hold the souls of the greatest heroes of the craftworld. A powerful force... and yet all but one of them are already dead. Rather evocative of the craftworld theme, is it not? As for the Young King... it is tricky, and I have not seen a conclusive evidence. I think that the current situation is that it is an aspect warrior, and that is that. If I remember correctly, in a fluff piece for the Eye of Terror campaign the Ulthwe Young King was an exarch. DoW has exarchs as the Young Kings, but the games are not known for being sticklers to canon (I wish MY warp spiders could get haywire grenades). It could be that it does not really matter and is a matter of choice and/or craftworld tradition.
It was effectively presented in Gav Thrope's Path of the Warrior as being similar to the Phoenix Lord suits, where the spirits of preceding owners would blend together over time. Usually with the original wearer being the dominant personality but with some strong aspects of the most recent bearer remaining strong for a time. I'm afraid I cannot comment upon how it was presented in the most recent codex but there do seem to have been a few minor changes which put Thrope's depiction in question.
