KURIOS and QEOS are not synonyms. Therefore, its possible for God to be Lord and yet it is also possible for a lord not to be God (or a god). For example, Abraham was called "lord" by Sarah (1 Pet. 3:6). Does this mean that he was also her god? Tertullian wrote in Adv. Hermogenes that God became Lord and Father when he brought forth his Son (Part 3). Thus while I would not deny that a QEOS can also be a KURIOS--even Jesus is likely called both in John 20:28--I believe that Paul intentionally made a distinction in 1 Cor. 8:5, 6 between QEOS and KURIOS. One source I will quote is the Interpreter's
Bible. Commenting on 1 Cor. 8:5, 6, Clarence T. Craig penned the following:
"Paul chose his prepositions [ex and dia] carefully in order to distinguish
between God the Father, who is the ultimate source of creation, and Christ,
the Lord, through whom [dia] this activity takes place . . . it is perfectly
clear what Paul wants to affirm. Neither Caesar nor Isis is Lord, but only
Jesus Christ. When Paul ascribed Lordship to Christ, in contrast to later
church dogma, he did not mean that Christ was God. Christ was definitely
subordinated to God" (Craig 93-94).
For proof of Craig's assertion, see 1 Cor. 3:23; 11:3; 15:24-28. The corresponding word for "Lord" in Latin is dominus, whereas pater stands for "father" as it does in Greek.