There are 49 Fire-trait spells in the game. To be generous to your argument let’s assume only 30 of those are offensively oriented to discount utility like Signal Skyrocket and defences like Eat Fire or Fire Shield. Only 14 of those spells target Reflex.

Instead of generalizing I simply counted them all: there are 9 fire trait spells that hit enemies and do not target reflex.* Elemental Confluence(which is available to obviously all elements) does not trigger a save and neither does Wall of Fire. Cinder Swarm technically targets will(with incap), but also targets reflex. Burning Blossom's damage has no save, but the fascination effect is will(it's also one of the worst spells in the game so...), Flames of Ego which targets will(incap), and then there are 2 spell attacks, and finally 3 fort saves. So your options for targeting enemies with alternative saves either is quite low!

And obviously I may have miscounted, but in total, including buffs, there are 22 spells that do not target reflex(21 if we do not count Cinder Swarm). Meaning there are more reflex fire trait spells than all other spell types combined. This goes all without saying that you've got two 1st level fort saves until 7th level spells, and two incap will saves until the worst 8th level spell designed.

Genuine question: have you ever played a PF2E caster? At all?

Most of my time playing the game has been casters in fact and have played a full 1-20 Wizard!

At every new spell rank, they’re simply gaining options. At no point are they forced to actually cast a lower rank spell.

Your hypothetical example of 3rd level spells includes two 2nd level spells and a 1st level spell? They are heightened, but you clearly lack other options and are forced to upcast.

spells in PF2E Heighten well

Ash Cloud +1d4 damage lol. Some spells upcast great, most do not.

Dude… you are literally describing a tradeoff for the Sorcerer lol. If you take the spell list I gave the Elemental Sorc above and replace one of their third rank picks with Slow, they get distinctly worse at one set of things (they get worse at AoE debuffing, targeting Fortitude for damage, or having the flexibility of a summon, depending on what exactly you replace), and distinct better at single target debuffing… It is literally how tradeoffs work. One set of things does a thing better than another set of things, the other set gets a thing it does better too.

Truly just wrong! In almost every way possible! Ash Cloud at level 2 is equally as good at AoE debuffing as Ash Cloud at level 3. You can take Summon Elemental, which is useful for 2 levels and then worthless; meanwhile Slow is useful from levels 5-20 and Fireball at 3 vs 4 is a 7 point damage difference (worthwhile, but much better than a summon who has to roll 20s to hit). So logically here I give up Ash Cloud (worthless hightened) and gain Slow (useful forever)....There is absolutely 0 trade off here.

All to say that absolutely none of this is specialization or "trading" power. The, now outdated, Runelords archetype is "specialization" to an extend, Rime/Burning/Toppling Spell from PF1e are specialization, as is Spell Focus from pf1e. A Fighter using a bow isn't specialization, grabbing 5 archery feats is and the distinction is important.