Learned Magicians aren't going to be blasting pilums of fire or similar spells, but they can hand out Virtues and give bonuses and eliminate botch dice. All things Hermetic magi can't do. And those can be very useful if they're prepared.
It's like wondering why the Justice League lets Batman hang around when he's just some guy without superpowers. A prepared Learned Magician makes the belligerent Flambeau sad because he's given himself Greater Immunity: Fire. And maybe buffed up the Great Weapon skill of his buddies who're whomping Flambeau's grogs. But if he's your friend he'll hand out lots of fun Virtues: Second Sight, Venus' Blessing, Luck...
And to add to this, and reiterate what was stated above; Learned Magicians can, through their Charta, respond faster to most situations and problems more or less on-demand.
A Cunning Folk magician I played was more specialized towards Charms rather than Chartae, but even with that, when all the associated bonuses are applied, he could pull off a charta of any form up to 4th magnitude. For Fortunam and Magicam forms, this is the point where you can comfortably start granting Minor Virtues (of General and Supernatural variety).
The effect Parameter's calculation is actually cheaper for Chartae then standard spells (chartae only have a Touch range, but it's free, Group and Sun cost 1, Moon and Bloodline cost 2)
allowed him to have some form of makeshift solution to a problem that could last for a month or a season, all with but a few hours of preparation. A magician with Strong Amulet Magic could do more.
And granted, while offensive usage of most Fortunam magics requires penetration to work, defensive and utility options are Godsent - reduction of botch dies, soak bonuses through the roof for that specific type of troublemaker you are dealing with, bonuses in social situations, etc.
That was true for fourth edition Learned Magicians (though they could cast spontaneous Rituals, which was a pretty big deal).
In 5th edition, for some reasons, Learned Magicians (and Cunning Folk) are mechanically very similar to 4th edition's Cunning Folk, basically granting Virtues, Flaws, and other bonuses/penalties.
I have to second what was said by others: any supernatural tradition that can grant arbitrary Virtues relatively quickly and without the need to research a specific formula (for Learned Magicians, this means Formularies and Chartae) is very powerful.
Wait -- does this mean such effects (being less than 6th magnitude) do not count as 'powerful supernatural effects'? Can Amulets, Chartae, and Charms be specifically tailored to reduce warping?
Generally it is 6th magnitude effects that constitute a powerful supernatural effect for the purposes of Warping. You can make a 6th magnitude chartae, but this is gonna be a bit more difficult.
I do not know about Charms, but I am fairly certain you can tailor a Charta or Amulet to an individual, since you can get hefty Lab / Charta total bonuses if you include a horoscope to a target. IIRC, if you use that bonus, then the Charta / Amulet will only work for that specific target.
Sounds like "tailoring the effect" to me!
EDIT: Actually, I think you need to include the Astrological Bonus if you're a Learned Magician. It's the Cunning Folk variants that do not have to do so.
The magi-
cian always specifically designs an amulet or
charta for a single subject. Should someone
other than the original subject attempt to
utilize the device, it provides no benefit to
the person.
Yes, folk witches have a niche, but traditionally, until the witch trials, they were the local healers and seers (one element completely missing) and the women that you never wanted to cross. For instance, we now know that the social status of folk witch traditions in the Nordic lands wasn't just a group of cast-out "strange" women but had a very high, sometimes wealthy status, sometimes to the level of bard. The something has been found in Nordic influenced lands (NE europe) as well.
Those witches living, just outside the village would have a respect and status equal to the local lord. With even the lord sending a contact for a discreet meeting as required. The power is not the magic always, sometimes it's just the people.
Well "folk witches" in irl history and "Folk Witches" in Ars Magica terms is not equal things.
Cunning Folk with Mystic Herbalism as addition is more effective in general healing (they not limited by vis). And have a lot of abilities that made you not want cross with them.