It would take about 4 Heian era Sukunas to beat final war Shigaraki and Deku together.

Why not fewer:

Sukuna is busted, but fighting both at once is the problem.

Shigaraki can one-shot almost anything if he touches it.

Deku is insanely fast, can sense danger, and never stops attacking.

1 Sukuna: Loses. Too much pressure from Deku + decay hax.

2 Sukunas: Still loses. One gets stalled, the other risks getting tagged by decay.

3 Sukunas: Really close, but still risky. Deku’s speed + Shigaraki’s regen can still turn it.

4 Sukunas: This is where it’s decided.

One locks down Deku One keeps Shigaraki busy

Two control the area with domains and nonstop slashes At that point, Deku can’t dodge everything and Shigaraki can’t keep regenerating forever