Advancing the Timeline

[Osprey]

I DO like the notion of characters needing to cultivate their reputations but why require this only of spellcasters? If wizards need to worry about what the rabble thinks about their spells, why don't warriors need to worry about what the rabble things about their swords?

While I don't quite hold with masterdaorin's 'fear all magic if you're normal' version of Cerilia, I have run into multiple instances in my own campaigns where fear and uncertainty are pretty rational reactions to magic use - particularly as PC spellcasters get higher level, and higher-level NPC casters also come into focus.

The most blatant form this takes is "Magic as a Weapon of Mass Destruction."
In my (Pathfinder) campaign, the PCs eventually reached 17th level and above. This included 2 Clerics of Cuiraecen as well as an elven Wizard, but it turns out that in 3e clerics at the highest levels are actually more powerful army killers than wizards (defying all the common stereotypes) due to a single 9th level spell: Storm of Vengeance. This spell has a 360' radius (and this can be doubled with a metamagic rod of Greater Widen Spell, which doubles the radius to 720'!).

A 2nd 9th level spell is Gate: which allows the caster to summon an outsider with up to twice the caster's level in HD. The cleric of Cuiraecen could thus summon a Solar (whose hit dice can be anywhere from 20 to 50 or more, depending how advanced they are, each with spellcasting powers of a high level cleric themselves - including storm of vengeance!).

Long story short: The Militant Order's 2 arch-clerics and the 2 Solar archangels they summoned could together conjure 4 Storms of Vengeance at once - allowing them to engulf and kill almost the entire 12,000-strong army of Ghoere invading Mhoried (encamped in a palisaded camp, and thus unable to quickly escape) in less than 30 seconds.

So as a DM I started talking about the rippling waves of consequence as news spread:
Magic like this completely shuts down regular warfare with mundane troops, and its actual use upon the battlefield - much like the use of atomic bombs in WWII - completely changes warfare forever in Cerilia.

It also deeply divided public opinion about the MoC: on the one hand, any who already disliked them now had ammunition to fan the flames of fear and paint the Stormlord (the MoC paladin regent and liege of the 2 clerics who were his Lts) as an arch-villain and mass murderer, honorless and utterly undeserving of Cuiraecen's favor.

On the other hand, a Mhoried zealot claimed to have visions from Cuiraecen. The man, a middle-aged farmer whose lands were pillaged and family abused by the invading Ghoereans - preached that the Stormlord was the ultimate Champion of Cuiraecen, chosen by the Stormlord's own hand to deliver the people of Mhoried - and indeed all the faithful of Anuire - from all the villains and ravagers of the world. At long last, the gods had sent a savior to deliver them from the great evils of the world.
(The PCs later kill the Spider and Rhuobhe, which greatly bolsters these claims and multiplies the faithful believing in this prophecy far beyond the borders of Mhoried).

Beyond these popular opinions and the deep political and religious divides that are formed, this also shifts the basis of military power being defined more by who has the greatest spellcasters on their side than whose armies are biggest or better-trained. It doesn't really matter if your 20,000 troops are typical 1st level warriors, or elite veteran warriors or fighters averaging 2nd-4th level - most battle magic is going to kill or severely wound them in a single hit.

High-level magic undoubtedly dominates average people in almost every way - be it overt battle magic or subtle enchantment magic like charm, suggestion, and domination. If you are a mundane person unlikely to survive or resist magics like this, you are definitely going to fear them!

But- much like WMDs - if you are part of the team that has them - you are going to be really damn glad your team has them, even if you fear your enemies have them too! So fear also mixes with respect and admiration for that power when used for the benefit of you and yours.

If as a DM you have people react tribally, I think you are going to capture the essential human reaction. If they trust the users of great powers to act for their benefit, they will probably be a fan. If they feel they cannot trust said users, they will probably be a hater. Fear of acting against them might still keep the haters in line, but such folks will always be ripe for recruitment by enemies of the magic-users who convince them there is a way to control or be rid of them.

Final Note: Even if you don't have high-level casters in your campaign (though you as a DM would have to erase most of the D&D magic norms as well as the high-level NPC casters in the setting material to not have them at all), a 5th level wizard can throw a fireball at a tight-packed infantry formation and annihilate several dozen hardened soldiers in the blink of an eye. So you can consider it pretty likely that the average soldier will really dislike, fear, and/or hate magic just like a 20th century soldier would hate few things more than land mines, artillery, flak, snipers, or poison gas - some of the things that make it so survival on the battlefield is less about skill and more about luck.

Allow a Wand of Fireballs in your game, and you can multiply this firepower many times, even in the hands of a 1st level character if they can use the wand!

Likewise: Charm Person is a 1st level spell. Suggestion is even more potent in its ramifications, especially in political situations, and domination most of all...particularly when you realize what it could do in combination with a ceremony of Investiture! You can be sure that having a good magician, mage, cleric, bard, and/or magic items protecting a regent becomes an absolutely essential tool to ensure a regent's safety and free will in a world where such magic exists - nevermind the potential of such magics to mess with your enemies!

Different editions of D&D keep revising the magic more than any other part of the game because they know it is the most unbalancing aspect of D&D, a fact that becomes more apparent as characters rise in level.

As a DM you can either roll with it and adapt your game to suit, or you can try to trim most of it out to try and keep your game as mundanely human and low-magic as possible. I think there are pros and cons to both styles of game.

My own preference (highlighted above) was to try and use D&D (and later Pathfinder 1e) mostly as-written and instead adjust the psychology in the setting to fit a world where such powers exist. This made for a lot less changing of the game rules as a DM and for players, which allowed me to concentrate on the already-immense workload of running a game that has detailed adventures and a full domain-level game. Heavily customizing the D&D rules has always felt like too much extra work on top of everything else a full Birthright game entails.

There's certainly a lot of issues keeping PCs and powerful NPCs relatable to us regular humans as they become high-level superheroes - a problem that exists in every version of D&D and many other fantasy RPGs. But at the end of the day, all of my players have enjoyed imagining what that might be like, just as huge numbers of people enjoy good superhero, anime, and other high fantasy stories. It's not the only kind of good fantasy, but it's definitely a viable one, just as gritty low-magic fantasy can make for good stories of a different type.