Arcane Harmony, Radiant Spark, Thermal Void, and Sun King's Blessing are all net negatives in making the core combat loop and rotation flow feel good; they actively go against it and make all rotations feel worse.
Arcane
Arcane Harmony ends up getting in the way of establishing a perfect sense of flow and ends up making the Arcane mage opener feel a hell of a lot clunkier than it should be. I understand the point of what Arcane Hamory is trying to do, but ultimately I feel like it contributes more toxic gameplay than healthy.
Radiant Spark also overlaps with Touch of the Magi, and their disjointed CDs end up screwing with the player as they flow between the conserve and burn phases. I would instead give both spells the 'Arcane Surge' treatment. Keep the talents where they are, but make them all passives and build up and make Touch of the Magi even stronger with a longer cooldown that aligns with the 1.5-minute cooldown of Arcane Surge.
Frost
Thermal Voidboth contributes to the same problem. Frost feels lost right now, trying to juggle three different playstyles, Icy Veins, Glacial Shard, and Ray of Frost. So my problem with those two talents is less about them existing and more about them contributing to the class design in an overly intrusive way that prevents the other styles from shining. I think some streamlining could be beneficial here, making Glacial Spike contribute and provide benefits off Thermal Void. Allow Glacial Spike to extend the duration of Icy Veins by a factor plus the cast time. Icy Veins does not need to clash with Glacial Shard, and the two can still easily benefit from one another.
As far as Ray of Frost, probably the single most ignored spell by mages since detect magic. Rework this thing; no one uses it; try and fold it into the mass AOE gameplay. Let each pulse burst and hit everything in a radius around the target. Let frost mages feel like they're unleashing a real blizzard when they drop a Frozen Orb, Blizzard, and follow up with a Ray of Frost that freezes everything in place while it's all melted down. There's some real potential with this spell; the animations and effects are excellent, but it's been five years since it was added, and it's never seen widespread use. Go back to the drawing board, and rethink it.
Fire
I don't play fire all that much, but hard-casting pyroblast is not fun, breaks the flow, and does not add as much complexity to the game as you think it does. It's an anti-fun talent that goes against the core design principles of fire. Suck King's Blessing needs to be removed or redesigned completely.
There are my mage hot takes after playing the pre-patch of Dragonflight. Maybe at 70, some of these issues will resolve themselves, but that's how I feel about these new talents for Mages. Overall pretty fun for casual players, but just a few feel clunky, and it sucks how strong those talents are.