What does Stone Soreror lack in mechanics?
I hope they rename Stone Sorceror Metal Sorceror, it fits it's function better as it really doesn't interact with stone.
Pretty much everything. Its durability buffs do not make it a frontliner at all, and what it does get takes an action to activate and can be removed through being incapacitated. It's really MAD, since nothing about the class makes you better with weapon attacks, so you need either decent strength or dex to make that work, and dex doesn't synergize with your stone armor. So you need really STR, CON (moreso than usual, since it also affects AC), and CHA.
Its main 'swordmage' feature, which is obviously the real identity of the class, doesn't even come online until level 6, far beyond any other archetype. It can only affect one ally, only reduces damage from physical sources, and has a weird requirement of being on the same surface as the enemy to trigger the punishment, which is just asking for arguments with the DM.
Stone's edge is just an incredibly generic damage buff that doesn't really help a wannabe swordmage in any way, it just feels like they couldn't think of anything and decided to slap some damage on there and call it a day.
The level 18 feature gives you wider use of your Aegis, but not only will this not cover a typical 5 man group completely, but the teleport punishment takes your reaction so its usefulness is limited. Another flaw with the Aegis as a whole is that it starts out offering a decent amount of damage reduction, but the max damage reduction of 7 is pretty mediocre at level 20 unless somehow paired with resistance.
In the end, this is one of the cases where I get perturbed by wizards attempting to sneak what used to be a full class into an existing subclass; it just doesn't work and either the features aren't allowed to be robust enough due to the weight of the base chassis, or there's just not enough space to include all of it and stuff is cut by necessity. I think a clear example of this was the artificer subclass of the wizard versus the later full artificer subclass, I personally think they're worlds apart in quality and the full class does a much, much better job of realizing the artificer fantasy and mechanics.
