What are tiers?
Tiers are a ranking of how "powerful and/or versatile" the various 3.5 base classes are, with low numbered tiers being considered more capable than high numbered tiers. It's important to remember that certain caveats apply to the rankings:
- Tiers assume similar levels of optimization. Someone playing an optimized "weak" class (like a fighter) and using its abilities well may be a lot more effective than a poorly built wizard played by someone who doesn't know how to make use of its options.
- Tiers attempt to describe power over levels 1-20. Classes will generally be in their listed tiers immediately, though the gaps between tiers tend to be a bit smaller at lower levels.
- Tiers are based on published material only. Homebrew and house rules can and will modify the rankings of some classes or even just negate the entire ranking system.
- Tiers are based on relatively high-magic games. In a low-magic setting the rankings will be mostly the same, but the gaps between tiers will get a lot bigger, because magic items tend to be the best way for less powerful classes to cover up their weak spots.
- Tiers look at characters' ability to solve problems of any sort, not just combat.
We frown on link-only answers, so I'll go ahead and summarize the full tier list of all published classes, originally from here. Fuller descriptions of why each class is in its tier can be found here.
Tier 1:
Wizard, Cleric, Druid, Archivist, Artificer, Erudite (Spell to Power variant) — Can do anything and everything, often better than lower-tier classes that supposedly specialize in that thing.
Tier 2:
Sorcerer, Favored Soul, Psion, Binder (w/ online vestiges), Erudite — As powerful as tier 1, but no one build can do everything.
Tier 3:
Beguiler, Dread Necromancer, Crusader, Bard, Swordsage, Binder, Ranger (Wildshape variant), Duskblade, Factotum, Warblade, Psychic Warrior, Incarnate, Totemist — Good at one thing & useful outside that, or moderately useful at most things.
Tier 4:
Rogue, Barbarian, Warlock, Warmage, Scout, Ranger, Hexblade, Adept, Spellthief, Marshal, Fighter (Zhentarium variant) — Good at one thing but useless at everything else, or mediocre at many things.
Tier 5:
Fighter, Monk, Ninja (both CA & Rokugan versions), Healer, Swashbuckler, Soulknife, Expert, OA Samurai, Paladin, Knight, CW Samurai (with Imperious Command), Soulborn — Good at one rarely applicable thing, or mediocre at one thing, or simply too unfocused.
Tier 6:
CW Samurai, Aristocrat, Warrior, Commoner — Objectively worse at their specialty than another (often Tier 5) class, without anything else to show for it.
Tier 7:
Truenamer — Apparently received no actual playtesting, mechanics as written simply don't work. See this question for more details.
Honestly, I see that you're trying to be two things, and this might be a bit of splitting point on your build, so I have what I hope is a good and sensible option.
Continue being split over two objective, but do it smarter
You use reformation to Psionic Body, Additional Traits, Power Penetration, Great Power Penetration, Spell Penetration (Mythic), and Persist Power for Psicrystal Affinity, Psicrystal Containment, Burrowing Power, Delay Power, Enlarge Power, and Extend Power. Additionally you reformation away all your offensive powers that allow Power/Spell Resistance away for alternatives that don't allow this defense.
This will let you start fights with a Extended Astral Construct, and let you manifest your blasting power in a more versatile way. While it does lower your options of powers to use, you can use your good selection of Metapsionic feats to make powers fit the situation, and you can apply two of them if you need to, as your glowing rock buddy can hold some of your psionic focus for you.
Best Answer
Tier 0 isn’t really a thing—JaronK’s tier list enjoys a lot of consensus, but only includes tiers 1 through 6. That list mentions the truenamer as being basically broken and not really fitting into the tiers, which is sometimes referred to as tier 7 (or simply “truenamer tier”), but beyond that there are just the six.
Furthermore, for the most part, the tiers very much want to treat classes by their full range of potential—from the naïve no-op build to a full to-the-hilt optimized build. The idea is that for a given amount of optimization, higher-tier classes are more versatile and/or powerful, and lower-tier classes are less versatile and/or powerful. The main point here is that generally speaking, class variants and options aren’t considered separately in the tier list—they just represent more or less optimization. There are a few exceptions—dungeoncrasher, for example—but for classes that are already tier 1, an option that makes them more powerful isn’t really considered relevant.
That hasn’t stopped people talking about the idea of things that are even stronger than what we think of as tier 1. Psionic artificer is notable for having dramatically more versatility than a regular artificer—which is already an incredibly versatile class, even by the standards of tier-1 classes. That’s notable. Sometimes the psionic artificer is therefore called as tier 0, or as the link offer suggests, “If there is a Tier Zero, Psi Arty deserves it.”
Spell-to-power erudite is also a frequent candidate for tier-0 status. Again, we’re talking about a character that has dramatically more spell access than a cleric or wizard, plus most of the power access of a psion. This thread has several people calling it tier 0, for example.
But ultimately, none of these things have even remotely the consensus that the main tier list has. Tier 0 isn’t really a codified thing, it’s just an occasional topic of conversation. Psionic artificer and spell-to-power erudite are some of the most common choices for those conversations. I don’t think you’ll find many people who will say “no, that isn’t tier 0!” though.