Worth mentioning that the ten shadows technique requires two-hand signs to invoke them. Megumi doesn’t have reverse cursed technique, and as a cursed spirit Sukuna shouldn’t either. Megumi’s deer summon has reversed cursed technique healing but he can’t summon it one-handed.
With the opening salvo alone Gojo just cut off half of Sukuna’s abilities.
Update: my bad, folks! I’d forgotten that Sukuna used reverse cursed technique to resurrect Yuji from a mortal wound after the cursed womb arc. So while the ten shadows technique is unusable right now, if Gojo lets up Sukuna will be able to recover.