Low lethality system: you deal 10 damage, enemy has 150 health, you kill him in 15 hits. After levelling you now deal 12 damage and kill the same enemy in 13 hits. 13 is clearly lower than 15, player feels progress.
Actually, most low lethality games makes you deal less damage in percentage to the enemy at higher levels. For eg, on 5e a Mage from lv 5 to 11 on 5e goes from 8d6 damage(fireball) to 10d6(freezing sphere), while his hp goes from 5 (d6 + con mod) to 11(d6 + con mod), that is just 2d6 damage gain and ludicrous 6(d6 + con mod), with no con mod, he got 3x more hp than damage. I an not saying that 5e is low lethality as 4e, 5e is in the mid ground of 2e and 4e in this aspect(lethality), but is rarely played at high levels and many DM's say that is hard to challenge a high level party. And 4e is actually worst and far worst in this aspect.
Is a tabletop wow clone in low lethality.
I honestly don't know any low lethality game where high level gameplay is quicker than low level.
How to take something with flavor and make it another boring "it does damage" spell.
Yep. This is why spells on his games are awful. I mean, there is any reason to pick any specialization besides evokation on pillars 2??
Note that on 2e, most iconic mid level spells, does far more than just throw damage numbers. Stoneskin, minor sequencer, wall of ice, polymorph Other, polymorth self, chaos, cloudkill, animate dead, teleport, enchant item, domination, disintegrate, tenser's transformation, death spell, teleport, flesh to stone, control weather, all of this spells are much cooler than any pillars 2 spells. Not mentioning the summons spells, allowing you to use a fire elemental to tank a fire creature.
high lethality and small numbers.
Is that generally JRPG's don't try to make the game mechanics a "translation" of things and IMO, numbers needs to be small to have meaning. Ultra inflated numbers is just silly, like ultra inflated currency. I like 2e D&D cuz a lv 0 commoner has d4 hit points and Vecna, a demigod lich has 150 hp. Meredoth, a lv 20 necromancer? 50 hp. Even dragons rarely goes on lower 3 digit hp. And is easy to grasp what the numbers means, 10 of a attribute is average. 7/8/9 is bellow average, 11/12/13 is above average and anything above 18 is superhuman.