Well, you said:
When methodological materialism is a belief, the one so believing is ill.
If you'd said "When materialism is a belief, the one so believing is ill."
That would have a plain meaning.
"Methodologcial materialism as a belief", using "belief" theologcially, I get something akin to saying mathematics is a religion.
I would however say that the unreasonable effectiveness of mathematics is God’s copyright notice on the Cosmos.