You can tell that Rockstar made a last minute change when it comes to the Pegorino family. Ray's supposedly a capo - he's got his own crew, he orders people around, he's the liaison with the McReary family, and the LCPD database supports it. Everyone talks about him like he's the big greedy boogeyman who'll do anything to get ahead, and people respect him out of fear. He's bossy, he owns front businesses, he has the air of someone who knows their sh*t and takes no sh*t from anyone else. The first thing to notice is that despite the fact that I'd say he looks like he's in his mid 40s, the LCPD database has him born in 1976. I highly doubt a 32 year old would be a capo in any crime family, even the Pegorinos.
In Phil's strand of missions, he and Niko talk about how Ray is the greediest motherf*cker around, a rat willing to betray anyone for a buck and some temporary prestige so that one day he'll reach Phil's position in the family. Little issue - Phil's only an associate, the lowest order in the pyramid. Ray, the capo, has already gone from associate to being made to being promoted to capo - if that's the case, he's already a sh*tload more influential than Phil will ever be. Adding to this is Jimmy's comments in Pegorino's Pride that the family is losing even more respect from the five families because Phil - the Irishman - holds such a high position in the family. Mafia families need people like Phil (mixed Irish-Italian) to hold down the fort. Henry Hill was mixed and so was Jimmy Burke, two of the most memorable mobsters of the past half century - it was commonplace. Jimmy's comment would only make sense if Phil had been made (i.e. soldier, capo); that would indeed be sacrilege to mafia tradition. Then there's the little details - when we first meet Phil in No Way on the Subway, he seems to be in charge of the conversation between Ray, Niko and himself - telling Niko that he and Ray are gonna have a problem, and taunting Ray that he keeps forgetting to tell Jimmy about things he's working on. Also, Phil's nine years Ray's senior - it would make sense that the older one would hold the higher position. Jimmy always talks about how Phil came in first, he's always been a trusted friend and his closest adviser, while Ray is the slimeball trying to work his way up the ladder no matter who he pushes off on the way. That considered, why would he have Ray made and keep Phil back, while at the same time griping about how he shouldn't have given Phil such a high position?
And yet despite all this, Ray is officially the capo and Phil the associate. They put this in plain words in Pest Control, when Ray taunts him about it. I believe that the two of them were originally opposites - Ray was the dirtbag hustler who would do anything to get ahead because he wasn't getting attention - all the work he puts in for Pegorino and he's still an associate. Phil was the capo - a complete violation of ancient mafia tradition - who always was the trustworthy one with Jimmy's ear. He follows orders, he's loyal to a fault, and he never wavers. If you wanna go a bit further with this, the whole Pest Control plot surrounds Jimmy thinking there's a rat in their midst, but it's never revealed if it was in fact Ray. This last minute flip by Rockstar considered, I think it's plausible that Ray was the rat after all - he's characterized as someone always pushing ahead no matter the cost, so when he sees the Pegorino family falling apart, he jumps ship. I don't know if he would go to the FIB or turn to another family, but it makes sense. As Jimmy says about Ray in his first mission: "Only way you know there's a rat is by finding their sh*t all over the place in the morning." Indeed - when Niko takes him out, the sh*t is all over the walls - the Pegorinos are reduced to nothing. After Ray's in the dust: "Cleaning house is a tough job, Bellic. I don't got much left in mine, it's so clean."
That said, I also agree that I never found Ray to be particularly cutthroat or slimy. He was brash, loud, confrontational - but he always upheld his part of the deal, and in the process got screwed by Johnny K, Niko, and ultimately his own boss. I think you can tie that into my theory above; despite how people perceive him, he was always the victim. He cared for Ashley, he helped Niko find Florian Cravic, and Jimmy even says he's his best earner. And despite all these traits everyone thought he was a self-serving sleazeball - at that point, what's left but to rat? He goes through his entire life being called a rat, and ultimately it comes true: driven by those very comments. Talk about a self-fulfilling prophecy.