We are not dealing with a quantifier or adverb.The source words of a compound adjective individually can be "adjectives, nouns, quantifiers, participles, and adverbs." Yet they are working as one unit in an adjectival manner.
English Compound AdjectiveIn a compound adjective beginning with a noun, we would be looking at a juxtaposed adjective or participle verb. Some examples of a noun + adjective construction are "sea-green, sky-blue, gluten-free." Examples of a noun + participle verb are "air-dried, wind-swept" In the latter case, a verbal action is being described, and this is specifically the case you are insisting here. Participle verbs are verbs ending in -ed and -ing, and are often described as "verbal adjectives." In Romans 9:5, you would be looking at a compound noun + past participle verb. Already, we are in conflict with the Greek, which should not happen.
Greek does not allow a noun and an adjective of the same case (nominative) to function as a compound.Greek is inflected, which exposes further problems with your reading. The accusative case, not the nominative, allows a noun to act as the direct object of a verb or the object of a preposition. The genitive case can also act as the object of a preposition. Because ὁ Χριστὸς is in the nominative, and θεὸς is in the nominative, θεὸς cannot modify ὁ Χριστὸς in that way. One or the other needs to take the accusative case for this to happen, and a verb will be involved. For example:
Ο Θεός (nominative) ευλόγησεν (verb) τον Χριστόν (accusative)
"God has blessed Christ"
"God has blessed Christ"
Ο Χριστός (nominative) είναι ευλογημένος (auxiliary verb + verb) από (preposition) τον Θεόν (accusative)
"Christ is blessed by God"
There is nothing in the grammar that allows a juxtaposed nominative noun and nominative adjective to act like a compound. We have two generic options in this case: (1) convert θεὸς into the accusative θεόν, or the genitive θεοῦ, and involve the verbal form of εὐλογητὸς (εὐλογέω) together with a preposition, or (3) dramatically rewrite the sentence where τον Χριστόν (not ὁ Χριστὸς) is involved. As it is, εὐλογητὸς is in the predicate position in the Greek. That does not mean where it is located before or after the noun, it means it is placed next to a noun yet does not have the article.
Greek forms compound adjectives a different way, by joining words together. For example, αγουροξυπνημένος is άγουρος (unripe) + ξυπνάω (to wake up). A lazy, idle person is described as χασομέρης, from χάνω (to miss) + μέρα (day).
Because θεὸς follows in an attributive participle construction involving an equative clause, θεὸς is a predicate nominative to "Christ." That's just how the grammar works. We either bring it in as a predicate, "who is God over all" or as an apposition, "who is over all, God."
To the contrary, "a lamp (noun) bright (predicate adjective) enough to lighten the room" demonstrates a predicative use of the adjective "bright" that sets off a new clause without requiring the introduction of a comma or verb, which you insist cannot be done. English allows this form of construction, where the verbal equation (in this case, "that is") is implied. The same happens here where in English, just as it is in the Greek, "blessed" acts as a predicate nominative that sets off the clause "blessed forever."This is also why your "God Almighty" and "lamp bright" proposed analogies were worthless.