Ok, here’s the thing: the way SL was designed, with the covenants system and legendaries that each tend to support only one type of play style, ST, AoE, or cleave but very rarely more than one really threw a monkey wrench into the thereocrafting. There is just too much variance for sims to accurately predict anything and when you couple that with the very poorly designed raid and the additional RNG factor that M+ affixes introduce there is only so much predictive potential. All that is to say you really shouldn’t be surprised at the conflicting opinions coming out of different outlets like wowhead or icy veins.
I tend to personally look at real life numbers which I feel tell the real story. When it comes to covenants it is very clear cut. 72% of Arcane mages play NF, 12% are Venthyr, and it’s a roughly even split of 8% between Kyrian and Necrolord. This is after the covenant shake up but it more or less tracks with the previous alignment meaning that a very, very small percentage of players made the switch even though the other covenants became significantly better than their previous iterations.
What that tells me is (1) most people just couldn’t be bothered to change and rightly so because it’s a stupid system and (2) Shifting Power is just far superior to the other covenant abilities because it plays to Arcane strength/niche which atm is burst AoE. Meanwhile all of the other covenant abilities augment weaker areas of the spec, such as ST and Cleave, and it’s always better to play to a spec’s strengths than trying to use bandaids to fix its weaknesses. You just get better results that way.
As for legendaries, let’s be real, they are all terrible. For the most part they are weaker versions of their Legion counterparts or BfA Azerite traits and that’s true across the board. The reason why all the sims pick Temporal Warp as the top ST legendary is because that’s true on paper but not necessarily so in reality. It is also useless in solo content, like Torghast, and can really mess your group up in M+. You mentioned this isn’t your main which likely means you will only craft one legendary so this definitely shouldn’t be it. The only two remaining contenders are Arcane Bombardment and Harmony.
I went into SL liking Harmony the most and it was the first legendary I crafted and upgraded to max but I absolutely hated its play style. The fact that it’s always active unlike Bombardment which only tiggers at 35% health seems attractive at first but then you realize how tedious it is to get to max stacks and how annoying it is to have to ramp up your charges every time you drop them with the empowered ABarr. Harmony works really well with Radiant Spark (the Kyrian covenant ability) but, and this is key, only with perfect execution and you only see the huge numbers people mention when you stack all your cooldowns including RoP which I just refuse to use as a matter of principle. In other words you can only get those insane 100k crits (assuming ABarr even crits) just a few times in an average legit fight.
This leaves Arcane Bombardment as the only real alternative but while it’s amazing in AoE and fair in cleave fights it’s pretty bad in ST but the reverse is true for the other legendaries so you will always have that trade off and that’s not on you but rather poor design on Blizzard’s part.
Just to end on a good note, since this is just going to be an alt for you just do whatever seems the most fun for you and just say the hell with it to the meta. After all if Blizzard doesn’t care why should we?
