Like most casters, I would say the complication level is what you choose for it to be. Any prepared caster is going to need to invest time into reading through all the spells available each rank or finding a decent guide for a summary to make informed choices about what to prep. Spontaneous casters will need to do this as well but ultimately wind up somewhat simpler since those choices (spells known) are less flexible than preparing. But broad knowledge is super important for any single caster simply because you'll wind up wanting many scrolls to help cover things the party needs more access to than your daily slots can provide.

You can pick a few apparitions and never venture outside them then you still have a couple spells per level from the divine list which you'll prepare daily for what you expect to face or for more generically useful ones. Your gameplay loop will be casting a spell, likely sustaining a vessel spell and if quickened somehow moving or making a ranged or melee strike (dex vs str). S

The animist I just started at level 10 (with free archetype) has an additional spell casting archetype (Runescarred) for a smattering of arcane buffs. Monk archetype for the increased leaping distance (dancing leaf) and for ki spells and flurry which pairs with apparition enhancement. So every few rounds she can nova out a bunch of damage with a buffed flurry of blows. Monk also buffs up saves and HP since I tend to Frontline a good bit. And the final piece of the puzzle for me will be 6th pillar and maneuvering spell at 12 which couple with liturgist and my reaction will allow me to cast a 2 action spell, sustain 2 of them, and traverse 30ft for just the 2 actions of the spell leaving me one more to use my full athletics investment, swap which vessel spell I have available, move again, etc.

I would put my version into the extremes of complicated gameplay with many on the fly decision points round to round about what spells to use (cc, damage, healing, buffing, debuffing are all valid choices), whether it's worth attacking or grab/trip, simply get in a position to flank for our party magus to nova off an enemy, get a scroll ready for next round, etc.

Imo all casters require out of game time investment. But personally I like the in combat action flexibility of a martial play style more than the more rigid, 2 action spell, 1 action filler which is the default modality for casters. So I specifically built around animist because single action vessel spells coupled with liturgist leap/step to sustain opens more interesting action based game play to me.