I want to start by saying this is very well-written, and it seems you’ve brainstormed for this quite a bit, rather than the idea being a random thought that just snowballed as you typed. I applaud you for doing much better than most people that post things like this.
Now, to respond to one part at a time:
Spellhance: I agree that this shouldn’t be pushed for. Not just because it’s “not in the spirit of Classic,” but, as you said, there are multiple issues from the design point of Classic compared to WotLK - heck, even compared to TBC - that makes this extremely messy. You’d need gear with stats spread across almost every stat, which would probably end up being so low, as to not invalidate gear choices for any other class/spec that’s not a spellhance shaman, that you’d be gimping yourself horribly by doing so. If the gear were anywhere near decent enough that it would make spellhance worthwhile, you’d likely end up invalidating a lot of gear, with other specs & classes rolling on the same gear.
Stormbringer: Stormstrike is MASSIVELY mana-intensive, even more so if you’re trying to stack for melee damage and forsake intellect to do so. From this perspective, a 5% chance to reset the CD on Stormstrike - especially if this procs off Windfury, Lava Lash, Shocks, and Stormstrike itself, instead of just attacks - sounds like you’ll OOM faster than you can type /oom. One could argue “just don’t Stormstrike every time it pops, forehead!” Then I say: What’s the point of resetting the Stormstrike CD in the first place, then?
It seems like it’d be a very strong rune that would be worthless more often than not.
Sundering: It’s Shockwave from Prot Warrior in WotLK, with a higher AP coefficient, shorter stun, longer CD, and does magic damage(which, btw, I don’t like “Flamestrike” damage; I don’t know if this already exists in Classic, but I’d prefer it to just be Fire or Nature damage, just my two cents).
I’m not a fan of it doing magic damage, especially if it’s based off such a considerable amount of AP.
To make a comparison, Shockwave for warriors in Wrath is (75 / 100 X AP).
To make a comparison in SoD, Avenger’s Shield for Paladin does (366 X/ 100 + 0.091 X Spell power + 0.091 X Attack power) to (448 X/ 100 + 0.091 X Spell power + 0.091 X Attack power) Holy damage.
Last comparison, SoD shaman, Molten Blast: (X 72 / 100 + 5 / 100 X Attack power) to (X 108 / 100 + 5 / 100 X Attack power) Fire damage.
(All the above have Xs for multiplication because asterisks are causing italics.)
I may just not understand the formulae, but it seems like 184% AP is massive in comparison to any of these.
It’s also not a great comparison with Divine Storm or Whirlwind as these are based purely off weapon damage. Other than doing a massive amount of Fire damage purely off AP, it seems like a decent way to work Shockwave into Classic, even if it’s on a shaman tank instead of a warrior tank.
Balance Criticisms/Issues: Resetting Stormstrike: already mentioned above; it doesn’t seem massively viable because of how fast you’ll OOM.
(Side note: Wild Strikes does not proc off anything but auto-attacks for ret. Windfury procced off SoC in TBC and TBC Classic, but Wild Strikes is currently not proccing on SoC, nor is it proccing off Crusader Strike - don’t remember if it did in TBC - or Divine Storm.)
Sundering doing too much AoE damage: Comparing it to Divine Storm or Whirlwind and Cleave doesn’t really make sense. The first two are capped at 4 targets, and Cleave only hits a second target. As you wrote out Sundering above, it would be uncapped. Aside from that, it really doesn’t seem like something tailored to dealing damage, first and foremost, with it having a 40 sec CD. Which leads into…
AoE CC on 40 sec CD: You specifically wrote in a line, rather than a cone. It’s a lot less likely that you’ll get nearly as many enemies in a line than you will in a cone. Doesn’t seem like it would be a massive issue, though I may not be thinking through it fully.
Outro Metrics: I’m not a fan of using 95% performance level from WCL, as most people will never hit that level. I prefer 75%, as this is much more reasonable for most people. That having been said, my post is already getting way too long, and 75th percentile vs 95th percentile only slightly shrinks the gap between the top at (warrior at 95th, rogue at 75th) and enhancement shaman from a 28.75% difference to a 23.15% difference, so I’ll just say: Yeah, the class probably needs some help, but they’re by no means alone in that sector.