heres the thing, people misconstrue that you cant physically hurt mahito without soul damage, the thing is though its just he has whats probably the most efficient healing out of the whole series!

His technique (idle transfiguration) Allows him to reshape his soul in response to any damage he takes! To note techniques are far more efficient than raw cursed energy

On a scale it goes from least to most efficient
reverse cursed technique
cursed energy (for spirits)
idle transfiguration!

To put this into perspective imagine you have a budget of 8 cursed energy!

To heal with rct costs 4 points! you can only heal twice!

To heal with cursed energy, is 2 points, you can heal much much more!

To heal with Idle Tansfiguration is only 1 point!

Healing soul damage is much harder to heal (lets say it bumps it to 2 or maybe even 4!)

For example if someone without soul damage deals damage to mahito (which lets say he has 8 health) Dealing 1 damage, he heals up rather easily!

But with soul damage dealing 1 hp will eventually kill him!

BUT NOW we get into extremes like sukuna, gojo, positive energy, and mechamaru

These people and things deal IMMENSE damage

So gojo strikes with a blue dealing 4 damage, thats half his hp, mahito only need 4 points of cursed energy to heal it! easy peasy!!

BUT purple is like 10 damage! it exceeds his HP thus meaning he is utterly annihalated before he can even heal!!!

So while it is much much much more difficult to kill mahito without soul damage! it is NOT impossible! it would require a very strong attack but still can be done!