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.

Artoria Caster = Her during most of LB6

Artoria Avalon = Her after her sacrifice to beat Cernnunos, turned herself in the embodiment of the sacred sword

Strength wise:

Castoria: While alive she's stated to be on par with a LB king and is stronger than Barghest after 6 bells, who for context is stated to be stronger than Gawain and could nuke a city with Black Dog Galatine. Her magecraft versatility and skill isn't nearly as good as someone like Medea, but she's still pretty competent with simple stuff like bounded field and her buffs are also simple but are pretty nuts in strengths. As a servant she's nerfed to some unknown degree but is definitely weaker than her living self (this applies to almost every servant)

Artoria Avalon: She's got everything Castoria does but better and with a little extra. She now has more close quarters capability due to her holy swords, Marmyadose in particular is stated to have even more raw power than Excalibur, though I don't think she can bring out all of that power out. She can also fly now.

Morgan: While living she has access to her throne (which has access to hundreds of years of mana) and 12 already prepped Rhongomyniad cannons (each one of which is equal to Zeus's thunderbolts, which in turn are stronger than Artemis's anti-planet cannon). Her magecraft level is top 5 in the world, which means she's extremely versatile and skilled. As a servant she's directly said to have 1/3rd of her original power and she doesn't have pre-prepped Rhongos or her throne and all its mana (though she can still summon Rhongos, just weaker).

Aesc: She's younger Morgan. Probably on par with Castoria, though better at fighting due to actually fighting close quarters with her spear. Morgan does imply that her undergoing several pilgrimages is what makes her far more powerful than Castoria, which she would've undertaken as Aesc, therefore making Aesc > Castoria. Again, nerfed as a servant to some degree.

Oberon: His fighting skills aren't actually as bad as people think, he still held his own against Artoria Avalon, Super Mash, and Fujimaru combined. He's also got the power of the Mors King, which took Woodwose to beat (who could rip apart several people on the level of high tier Knights of the Round Table). His real strength however, comes from the Insect of the Abyss, which could devour all of Britain and is nearly inescapable. It puts anyone in it to sleep and traps them in an infinite space. As a normal servant, his fighting strength is pretty fodder and the Insect of the Abyss is smaller and weaker, easier to blow up but still more than capable of one tapping most servants.