Strength in Fate really doesn't work this way

Its not "X is stronger than Y" its "X beats Y under A circumstances because of B"

Take Shirou vs Gilgamesh. These are, probably the furthest possible gaps in power that you can imagine in the setting, and yet, Shirou wins. This isn't because Shirou is stronger than Gilgamesh, it's because Shirou happens to have the tools to counter Gilgamesh.

Almost any conflict in Fate is going to work along these lines of, "Who has the counter to the other" --> "Who thematically answers the other better" --> "Who has the greater Mystery/Concepts going on"

This is why we can watch Ritsuka engage a beast in straight up hand to hand combat. They thematically and conceptually answered Goetia, so were able to take them on.

If you want terms of raw power though, rather than comparision, Artoria Caster is the definition of an Outlier. She tends to roughly compare to a Knight of the Round. Artoria Avalon is a fully realized Artoria, with everything she would have unrestricted by class container, think Ichor Heracles.

Lostbelt Morgan is probably one of the single best maguses we know of in the setting, and does things that straight up rival true magic with relative ease, including taking down and destroying a lostbelt tree in a single shot and casually throws around world pillar scale spells.

Oberon is a defense mechanism of the planet that is intended to devour Britain. He is technically weaker than Morgan, but in practice is far more dangerous as he'll straight up eat all of britain and then threaten the rest of the world.

Aesc IS Morgan

Gareth is probably mid tier servant scale? She's one of the weaker KoTRs normally, and her fairy self isn't much better.

Artoria Lancer heavily depends on the context you are discussing her in, and has no reliable power level so to speak

Her third ascension basically makes her one of the strongest heroic spirits. Ever. She is the equal of Morgan in terms of raw strength at that stage as a servant, but not as a magus. Morgan is another breed of genius. Artoria Avalon as a Berserker just demonstrates that potential further, all her attacks are magical nukes. And her NP is basically a calamity that not only can reduce all of Lostbelt Camelot’s walls to ashes, but reduce (a god) to cinders. Albeit it was based on Morgan’s magecraft framework.

@The Legendary Vin

My meaning is how strong the characters (and also some explanation about Artoria Caster), not who wins in a fight.

Because it's hard to understand their full strength just from their pages.

@SpicyCookie

What do you mean by that?

Her third ascension in her caster class is her as her proper heroic spirit form. I wont go into detail about her ability but as a heroic spirit Castoria is the equivalent to the Throne of Heroes itself. She can freely summon anyone she wants as a servant, on top of possessing Excalibur as a magecraft theory as well as a legendary Holy Sword as an armament. Her power as a servant is equal to Morgan’s as a servant. The only difference is Castoria is more of a tank, while Morgan is more of a AoE genius. Castoria is easily one of the strongest heroic spirits we encountered in the Grand Orders. She can also create bounded fields with anti-purge properties (anti-purge is one of the strongest types of defensive ability to have as they are used to counter calamities and world destructive situations).

The description I gave is the powerscale for how strong Artoria Caster is. Specifically— Artoria Avalon.

Artoria Caster (1st and 2nd ascension) is not that strong at all. She’s a second rate Caster at best. Her ability as a Fairy of Paradise puts her above Nitocris and the likes for Casters, but due to her lack of creativity and talent in Magecraft she is kind of mediocre as a Caster.