In the Harry Potter anthology, we just know a few examples for each, as mentioned by the author. I discovered it was fun to categorize the various characters. Did this during a recent family gathering (with relatives who know about the wizarding world.)
Being a powerful wizard as opposed to being skilled is analogous with an intellectually gifted muggle as opposed to a muggle who spent years of disciplined study. Or, still with muggles, one with considerable athletic talent fighting an opponent with a high level of conditioning, technical ability, and competitive exposure. A powerful wizard might be measured by his/her aptitude for magical training, strength of his/her spells and jinxes, and ability to resist them. A skilled wizard would have high intelligence, an encylcopaedic knowledge of spells, potions and magical objects, as well as their applications. Magical power seems to “spell” the difference during combat.
Here are the skilled wizards and witches under my qualified ranking:
- Severus Snape
- Alastor Moody
- Horace Slughorn
- Filius Flitwick
- Dolores Umbridge
- Pomona Sprout
- Kingsley Shacklebolt
- Lucius Malfoy
- Mr. & Mrs. Frank Longbottom
Cedric Diggory (had he lived), Hermoine Granger, Luna Lovegood, Ernie Macmillan, Michael Corner, and Percival Weasley might eventually be categorized as such.
The powerful witches wizards are given below. The qualifications and rankings get more fuzzy down the rank:
- Albus Dumbledore
- Gellert Grindelwald
- Minerva Macgonagall
- Father and son Crouch
- Bellatrix Lestrange
- Lily Evans
- Viktor Krum
- Amelia Bones
- Molly Weasley
- Grandma Longbottom
- Antonin Dolohov
Among the budding wizards, I would qualify Neville Longbottom here. His abilities were decidedly latent but began to cement as he grew older.
Now the two I purposely left out:
First, Voldemort. He had great power, yes, and like Lily Evans, he can do focused magic as a child despite a muggle upbringing. But his personality and eventual direction point more to superior intelligence and acquired skill, rather than natural magical ability. A skilled wizard tends to be more jealous of his abilities (Severus Snape being a supreme example.) A “natural” is more relaxed with his powers and seems more accommodating with less talented wizards and witches.
Harry had great power for one with average intelligence. His natural abilities may have been accidentally acquired, as a result of the actions of Voldemort and Lily. But more important to Harry was his courage and loyalty. Those two qualities, I’m almost sure, are regarded by wizards to be magical powers, and possessing them in great quantities constitutes great magical power.