Arcane Magic didn't get "Stronger" because you defiled in 2e. It was just magic. It was weaker (took longer) if you preserved. So it created this important choice for you and your character.
It mostly did, because defilers had a much faster XP table than preservers (who used the normal wizard one). However, due to the way the XP tables kept doubling for most of a character's career, the effect was something like a defiler being about half a level ahead of a preserver until you hit like level 12 or so.
Neither affected the casting time of your spells, though defiling would delay the actions of everyone near you (which would usually be your own party) – even if sub-epic defiling magic couldn't kill animal life via defiling, it was still painful.
Lore-wise, there were some contradictory narratives. The one that seems to fit best is that when Rajaat originally invented arcane magic, he created both preserving and defiling magic, and in the process absolutely wrecked the region where he did his secret experiments. When arcane magic was then presented to the world, only preserving was presented, and clearly it wasn't obvious that you could do it in another way. As he found champions willing to do his genocides for him, he taught them defiling instead, giving them an edge over others. There one adventure, Dragon's Crown, where the PCs come across an ancient fortress from this time where forces from the preserver faction were being besieged, and one of them describes learning about defiling techniques and how it felt like putting a sail on a ship in how much easier it was.
So it seems that while defiling is easier than preserving (as shown by the XP table and various lore), it's not necessarily obvious how to do it. Then again, we have novels showing how the main wizard character does take these short-cuts without much trouble and skips back and forth between defiling and preserving, so it would also make sense that these techniques have become more-or-less common knowledge in the modern-day Tablelands.
Sure, you can define it that way,
most people don't but you can, and in that case, Dark Sun has absolutely never, ever, even for one second been grimdark, because literally first adventure, which came packed into the Dark Sun boxed set in 1991, features the good guys killing Kalak and fundamentally changing the setting. So what are you even upset about lol?
The adventure that came packed with the Dark Sun boxed set was A Little Knowledge, which starts the PCs out as slaves in a mekillot-drawn caravan wagon traveling from Urik to Tyr when said caravan gets attacked by an elf tribe as revenge for something. The elves then tell the PCs "I guess you're free now. Now go eff off." In the middle of the desert, with pretty much no gear. So it turns into a survival thing until the PCs eventually come upon a dwarf village where they can rest once they help them with a little something.
You're thinking of Freedom, which was a separate release but mostly simultaneous with the box set (I don't know if it was the same month or a month or two after, but one of the first releases). This adventure has the PCs arrive in Tyr and then contrives to get them enslaved via various means and set to work on Kalak's nearly finished ziggurat. The adventure then has them interact with various factions among the slaves partially depending on how they got enslaved, which then leads to connections with various factions in the larger city-state. Eventually the adventure culminates in some NPCs killing Kalak while the PCs try to escape the life-draining magic and (ideally) rescue some people as well – I've previously described this section as D&D trying to do a disaster movie.
Anyway, at the end of Freedom Kalak is dead and slavery has been abolished. The next adventure, Road to Urik, as well as the City-State of Tyr sourcebook explores the consequences of these events – while it's presented as an overall good thing, it's not without its problems.
In the first Dark Sun box, magic-users had two types which you were locked into. Preservers or defiles, where defilers were not much more mechanically different than preservers but they got a rapidly accelerated xp advancement table.
In the second revised Dark Sun box, the magic user class was re-imagined with a table that any character could choose whether to defile or preserve at the time of casting.
No, you were still locked into defiling or preserving when you became a wizard. The table you're thinking of was for defilers defiling when memorizing spells, with doing so in lush terrain having a chance of getting extra oomph and doing it in bad terrain giving less. I was never a fan of this, because it moved the defiling to memorizing at the start of the day. This would have some knock-on effects, chief of which would be sneaky defiling. OG defiling was a dead giveaway, as the defiler would be surrounded by a circle of ash when casting a spell. But you also had the lore aspect that most tribes had either a defiler or a preserver in a leading position, and that sedentary tribes would usually have a preserver because they don't like someone who bleeps where they eat, while raiding tribes would often opt for the stronger power of a defiler because they likely won't be casting much at home where it matters.
Something that just occurs to me - Paizo copped merry hell a couple of years ago over the Agents of Edgewatch AP. Having a campaign centred around 'good guy' law enforcement PCs was seen as distinctly smelly give the political events around BLM etc that were happening at the time. Paizo eventually had to put our a quasi-apology I think.
Agents of Edgewatch had plenty of other issues. Chief among them was that the cop PCs were pretty much unpaid, and were expected to subsist on fees/fines extorted from criminals (essentially traditional D&D "beat them up and take their stuff"), and that was... certainly a choice.
