Mass (and Holy Communion) quoad se (intrinsically or in and of themselves) have infinite grace. One Mass has enough grace to convert the entire world, and one Holy Communion to turn the most abominable wretch into a the greatest saint.
But not ALL of this grace transmits to or gets applied to souls. So, quoad nos, the amount of grace we receive depends on God's will. Nor is it necessarily just proportionate to the dispositions of someone receiving Holy Communion. So, for instance, saints have said that if an unworthy priest offers Mass, even if it's valid valid, let's say the priest is a grave sinner, a sodomite, child rapist, etc., then the amount of grace from the Mass that gets applied to the faithful is much less, if any.
So the difference is between intrinsic grace, and applied grace.
If a Satanist priest says a Black Mass, even if valid, I doubt that any graces will flow from that into the world. Instead, it's quite the opposite.
If a Catholic went to a Greek Orthodox Liturgy to receive Communion (let's say he didn't know that was wrong and committed no sin, subjectively speaking), there's nothing that says God has to apply the graces of that Communion to the recipient's soul.
There's no theological principle that dictates that God must apply grace from the Mass or the Sacraments to a soul at all, any more than there is a principle that God needs to apply 100% of the grace (if it weren't infinite and could be thus quantified).
So, again, assuming that 100% is the amount of grace intrinsically available from a Mass, God could dispense / apply 80%, or 50%, or 10%, or 3% or ... 0% of the grace. Johnson's misguided theory would hold that there must be grace given. So if God dispensed .000000000001% of the grace, that would comply with his made-up principle. We know that God does not dispense all of it. So, perhaps Johnson could come up with some math about how much grace God is bound to bestow.