The Archivist is a simpler situation. Archivists don't have the power to cherry pick off any divine spell list. That is not an ability that they have. Like the Wizard, they have the ability to learn from any piece of magical writing that the DM gives them. The DM might give them access to a really awesome spell, but they might not. And in any case, the Archivist has no ability to make that happen. It's not actually different from the rule that Wizards can scribe any Shugenja or Paladin scroll they come across into their spellbook and then start casting it (yes really, that's what the rules say). It's just that JaronK and a bunch of other people think this is going to happen to Archivists because Archivists are so shitty if it doesn't.
Or to put it another way:
- Barbarians are underpowered if they don't get an artifact ax.
- Therefore the DM is going to give them an artifact ax.
- Artifacts are really powerful.
- Therefore Barbarians are powerful.

So the "tiers" are completely meaningless. It's not all "raw" and it's not all "sensible" and it's not even consistent. JaronK has a completely arbitrary list of tricks he will let each person get away with based on what class they are and throws in completely arbitrary handicapping based on what he thinks each class needs and/or deserves, and then he rates the classes after having made all those explicit and implicit ad hoc adjustments. It's completely meaningless.
Saying something is "tier 2" or "tier 4" imparts no information. Since you aren't JaronK's girlfriend, a measure of how likely JaronK is to personally give you a DM pity artifact at level 2 is not something that makes any difference lengthwise or sidehow.
-Username17