This looks like a brew that would require practical experience to determine its power level, at least in my opinion, so instead I'll focus on qualitative feedback: I think there are some interesting aspects to the archetype, and I agree for sure that having more accurate spell attacks would be a desirable feature for many. My main criticism at this stage is that the way the brew goes about it is a bit too direct, with emphasis on self-empowerment, lots of bonuses, and a fair degree of redundancy given the collision of various fortune effects. More specifically:
Last Ditch Wiggling and Supreme Spell Attack are both fortune effects that also compete with True Strike, itself a fortune effect given by the dedication feat.
Virtually all of the feats grant some kind of number boost, including early advancement on the spell proficiency track in the dedication feat. Generally, archetypes that go about fulfilling a specific goal try to add effects that are somewhat more open-ended, e.g. an effect to make a target flat-footed/off-guard or the like.
Never Stop Flinging I feel could use a redo, as its wording assumes spontaneous casting by default and only then explains how it works for prepared casting, despite in my opinion providing a much greater benefit to a prepared caster.
My suggestions at this stage would be to try to do things in a slightly more indirect, open-ended, and team-focused way, ideally with stuff that injects flavor beyond just the basic idea of hitting really accurately with spell attacks. For example:
Rather than advance the proficiency track with the dedication feat or give out True Strike as an innate spell, you could implement Last Ditch Wiggling as a focus spell, letting the player reroll failed spell attack rolls.
You could give the archetype a single-action save effect that can render an enemy flat-footed/off-guard, or alternatively implement that as a spellshape option for your save spells so that they can complement your spell attacks.
You could have a feature that lets the character sacrifice lower-level spell slots in exchange for more top-rank spell slots (or one rank below the top) during daily preparations, so that the caster could dedicate themselves to blasting. You could even do something akin to the Summoner's Master Summoner feat and have this produce an extra amount of slots just for attack spells.
As a more far-out idea, you could have a feat that lets you plant your staff into the ground and have it give the option to grant its item bonus to any spell attack roll made adjacent to it at the expense of charges. This could let you boost your attack rolls with some level of risk (you'd have to stay within the same area and potentially bunch together), while also letting you support other casters.
The general idea being to hand out toys to the player that let them do a bunch of things that happen to boost their spell attacks, rather than directly hand out of +2s, +3s, or equivalent statistical benefits.
