You don't need a previous ranks to upgrade to rank 5 or 6. The only difference is soul ash is include in the cost instead of just soul cinders. So it is a negligible cost to change your legendary to a new slot if you were planning to upgrade to rank 5 or 6 anyways. It really is a non issue because as you are gaining soul cinders you are also gaining soul ash.
It sounds like Torghast just simply isn't for you. That is fine. It won't be something everyone likes. But it is hardly that bad and if all you wan to do is get some soul cinders as quickly as possible running lower then layer 12 is always the best way. A layer 9 can be done in less then 20 mins.
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Lol. There are other sources of conduit upgrades that you won't be farming Torghast for them. For someone that keeps calling the system, and game, garbage you sure spend a lot of time thinking about new ways to hate on the game. Weird huh?