I think the issue with Matrix is that going from vulnerable to invulnerable is a downgrade. However, if the invulnerability is "part of the contract", then you

I think the issue with Matrix is that going from vulnerable to invulnerable is a downgrade. However, if the invulnerability is "part of the contract", then you don't have this downgrade. You can also have low stakes with a vulnerable hero if you don't care about him.