What went wrong in 12.0:
Arcane missiles was tuned egregiously badly, cc generation was too low, Arcane Orb cdr was insufficient, and yet the whole rotation lived and died by Arcane Salvo. As a result you were stuck spamming Arcane Blast (or worse Arcane Pulse) in order to build salvo which is what powered the whole rotation, except spamming AB/Pulse is throttled by mana, so with bad rng you rotation just fell flat on its face because you couldn’t cast your builder spell, let alone your spender. Plus you know, lack of defensives, lack of mobility, lack of anything that a class requires in wow retail to be remotely competitive…
What I think works in the proposed changes:
Obviously missiles being back at the forefront of the spec is very welcome - assuming it is tuned well. It is incredibly important for the health of the spec that this happens through the base design, rather than a tier set bonus. High Voltage is one of the best additions the spec has received in years.
The new Apex talent basically doubles down on insurance for avoiding the crappy moments when you’re low on charges. Also it looks really cool and hits really hard. Between that, High Voltage, and the odd Arcane Orb, the “fall flat on my face if I have low arcane charges” issue with the spec is basically gone, and that feels fantastic.
For spellslinger Arcane Salvo actually works as a mechanic, courtesy (mostly) of Polished focus. Because you only need to build 15 stacks, and that takes a single AM cast+whatever filler at most, your rotation actually flows nicely. You hit max stacks a lot, therefore barrage a lot, therefore proc the apex talent a lot, therefore generate lots of CC, therefore you keep going quite easily.
What I think doesn’t work in the proposed changes:
For Sunfury, Arcane Salvo is a lot worse and these changes do not fully fix it - as in, it’s very similar to 12.0. You barrage less both because you generate fewer stacks (since you don’t have splinters contributing) and because you need to build more stacks before each Barrage cast, so you need 2AM casts per cycle vs Slinger’s one AM cast. If rng isn’t with you, you’re back to spamming AB, and you go out of mana, and you can’t cast spells, and you’re back to the current patch which we all agree is miserable. Possible fixes here include turning the CC generation of Sunfury up by a LOT (e.g. by greatly increasing the proc rate in Pyrocosm), and/or going back to a cap of 20 Salvo stacks for both hero specs.
Intuition still feels out of place. For Spellslinger it doesn’t really matter since you cycle salvo/charges so quickly, but for Sunfury it adds to the constraints above and is generally just an unsatisfying talent. If we wanted something to mix up gameplay, a better solution would be to turn it into a proc that says “your next barrage counts as having 4 charges and max salvo stacks, and does not consume either” or something. Just “hey freebie barrage” before moving on.
The tier set encourages counter-intuitive behavior. It is very common to cast missiles to build the last few stacks of Arcane Salvo you need to Barrage, but then you’re in a situation where you have the tier set proc (therefore, you want to cast Blast/Apex) but you also are at max Salvo/Charges and want to clear that with Barrage. Here your options are either a) barrage>blast, meaning you effectively wasted a tier set proc, or b) blast>barrage, which means you overcap salvo. The latter feels kind of bad, the former feels awful. An easy fix here is to just make the tier set buff Arcane Barrage as well, just like Nether Precision used to.
What else is missing:
This spec has a LOT of dead talents in this state, and these changes kind of double down on that - particularly in the capstone tier. Mana Bomb, Presence of Mind, Charged Orb, Evocation, Orb Barrage, Orb Mastery, Overflowing Insight and Charged Missiles are all unplayable, partly because of tuning, but mostly because their design fundamentally does not work with the spec.
Touch of the Magi and the miniburn are once again incredibly weak and near negligible with these changes.
Spellslinger still provides near zero defensive benefits, particularly because the Mirror Image talents do absolutely nothing.
Speaking of Pyrocosm, I am told it is still bugged and has a 0% proc rate. Which explains SF’s abysmall CC generation leading to its rotational woes. Might want to double check that.