One of the tenets of feudalism is that what power there is, is held by but a few people. These esteemed peers determine how this power is delegated out, demanding fealty and fearsome oaths to retain nut just that loyalty, but to retain the entire massive system of power. It is the same with wizards as it is with the nobility. The wizards are perhaps even more jealous of their power. Look at how few take apprentices, and how many of these apprentices themselves are sabotaged by their instructors so that they do not become rivals or enemies. A lord will train his son to take his place but a wizard will take everything to the grave and lay dread curses on anything they held so that a usurper is undone by their ambition.
The art of magic has been shrouded in mystery and dogma, with many of the nuances and variables in the spells having nothing to do with magic itself, and everything to do with shrouding the arts. Making them inaccessible, and elevating the few that know them to high social status. A sorcerer might be of mixed blood, but his command of magic allows him to stand eye to eye with a duke or even a king. These scattered practitioners of magic are involved in their own studies of the art, which is kept cloistered in towers and dungeons, until something goes wrong. Sorcerers are seduced by dark magic, make pacts with the wrong entities, and their cruel experiments escape to wreck havoc on the countryside.
Maestery is the simplification of magic. It does away with the moldy grimoires and the rest of the occultism of the art. A spell can be learned by any soul with sufficient will and intelligence, not those who just happen to be arbitrarily gifted with supernatural heritage or the aura of the fae, or pacts with devils.
What is a Maester?
A Maester is a non-specialized magic user who can cast spells from books and scrolls, and can use magic items.
Maestery? Nonsense. These maesters are pretend mages, who divest themselves of the history and tradition of magic. They are bakers who have learned how to make bread and crackers and think themselves the revolution and that they will strike down the boulangerrie and the patisserie. They are as pompous as they are foolish.
Maesters cannot specialize in any school of magic, and cannot cast their spells without access to their tomes and scrolls, aka Prop Dependency. Likewise, their ability to learn non-Maester spells (non-simplified versions) is at increased difficulty. Finally, maesters cannot research new spells, but can only reverse engineer existing spells into simplified maester forms.
What is a simplified spell?
A simplified spell has no dice and no variables, and functions the same every time it is cast. A regular magic missile creates 1-3 magic missiles that deal 1d4+1 damage each. The Maester's Magic Missile produces exactly one magic missile that deals 3 damage. Summoning spells function the same way, they will always summon the same number of creatures, with the same levels and abilities each time.
Maesters are able to learn magic quicker than traditional wizards and sorcerers, meaning their apprenticeships are much shorter. Maesters are also dramatically less likely to set up isolated fortresses, threaten the common good, rouse armies of undead, converse with demons, and otherwise fall into the majority of pitfalls that await traditional mages.
To the public, maesters are more wise men, sages, and otherwise benevolent and beneficial members of society, and are treated accordingly.
Simplified spells can be quickly and easily picked up, and the tomes of maesters do not require extensive deciphering.