He allowed Peter, Barnabas, and Paul to speak and then ruled on what to do.
The word is used for one who would judge or have the final say.
" 2919 krino (kree'-no);
properly, to distinguish, i.e. decide (mentally or judicially); by implication, to try, condemn, punish:
. 2919 krino-
5) to judge
a) to pronounce an opinion concerning right and wrong to be judged, that is, summoned to trial that one's case may be examined and judgment passed upon it
b) to pronounce judgment, to subject to censure, used of those who act the part of judges or arbiters in matters of common life, or pass judgment on the deeds and words of others
6) to rule, to govern to preside over with the power of giving judicial decisions, because it was the prerogative of kings and rulers to pass judgment "
"it is clear to me that James as an Apostle, is just supporting Peter's speech(Acts15:7-11) "
Whether James is agreeing or supporting Peters words is not important. The context of the verse shows that James, not Peter had the authority to make the final decision.
You can twist this anyway you like to get it to fit the RCC teaching but the verse supports what many scholars outside the RCC claim: James (half brother of Jesus) was the leader of the early Christian Church