I'm not defending the Darklight Wizard class. It is in need of serious editing. However, I was curious how it actually stacked up against our friend the Ur-Priest.
Basic Information
Thought Bottle: 20,000 GP
Darklight Codex: Minor Artifact, no cost, no CL
Staple Fastest 9s: Class 5 / Ur-Priest 9
9th level spells at ECL 14: 150,000 GP, 91,000 XP
Assumptions on acquiring and using a Darklight Codex in a campaign
1. PCs defeat a Darklight Wizard of 10th or higher level to acquire the Codex. Players themselves are at least 10th level with 45,000 XP
2. PC successfully uses Codex, and returns to a 1st level character
3. PC aquires 9th level spells at 9th level, or 36,000 XP*
4. Party is now at 91,000 XP, or 14th level. Ur-Priest has 9th level spells.*
*Does not factor in experience as a river, or the fact that the Darklight Wizard could easily face some death level loss setbacks being so low level and fragile.
Assumptions of actually being allowed to enter a new game as a Darklight Wizard
1. As a Minor Artifact, the Codex is at least 25,000 GP value
2. Character thus may only be created, and possess the Codex starting at ECL 13th or later, with a WBL of 110,000, single item costs no more than 1/4 WBL.
In this case, we do better than the Ur-Priest, although an XP penalty should be factored in as per actual acquisition and use. In fact, this sort of must be done in order to decide previous professions skill ranks and feats, and whether they could have actually made a DC20 Int Check and DC30 Will Save.
Conclusions
1. Given reasonable assumptions, it's not really that much better than Ur-Priest acceleration, in terms of when it's acquired, unless it is combined with other brokenness.
2. Thought Bottle smashes the XP cost with a GP tradeoff, commonly banned item. The Codex can only be used once by a person, so no looping, I believe.
3. Character ends up with 'free' feats & skill ranks from previous profession
4. Character may potentially be Darklight Wizard 1 / PrC X, which is sort of matched by extremely liberal character rebuilding.