I don't think that is necessarily the case with Bioware writers. They have certainly written some very "good" characters over the years. But, as I said before, every character needs some flaws to make them human.
Back to my previous Arthurian analogy Lancelot, and later his son Galahad, were both despised by many of the knights for their qualities as they were perceived as putting themselves above the rest of humanity ("The Once and Future King" and " Le Mort d'Arthur" are good Arthurian reads). One of my personal favorite musicals is Camelot, wherein Lancelot sings "C'est Moi" as he rides into Camelot, Guenevere replies to his arrogance with "Then you may take me to the fair," and later Mordred sings "The Seven Deadly Virtues". All flawed characters who superficially represent the spectrum from good to evil, but in truth are varying shades of grey set against a backdrop of Chivalry and Christian morality.
Even Salvatore's Drizzt is not without his flaws. He certainly succumbs to his "humanity" in later books as he teams up Entreri and Dahlia. I won't argue that Drizzt ever crosses the line and departs from the path of good - but he is certainly not a paladin.
On the subject of "good' characters, I would say DAI seems likely to have a preponderance of them. Cassandra, Blackwall, Dorian, and Sera all seem to have very noble goals and to possess strong moral convictions from what we know of them. Cole seems to be in the process of evolving his morality and his intentions appear to be good. None of the other characters seem likely to be classically "evil".
I enjoyed Wynne and Alistair as good characters, in part because of their flaws in DAO. But I would argue that we don't know enough of Morrigan's motivations to judge whether she was good or evil (I suspect the answer lies squarely in the middle), Leliana, in spite of her conversion and current appearance as an overtly good character, was not a virtuous character in her life as a bard. Oghren, in spite of his alcoholism, still tries to do what is right - although sometimes he fails spectacularly. In DA2 I would define Aveline and Bethany as "good" characters. I only did one mage play through and I don't remember my interactions with Carver that well, but he seemed decent. Anders is trying to do good (until he falls off the deep end), Varric is kind and loyal.
But I don't think any of the above Bioware characters (with the exception of Aveline) would fall under the D&D definition of lawful good.. Most would hit somewhere between neutral and chaotic good if you had to classify them. The remaining cast would fit somewhere in the neutral spectrum. Can't think of any I would define as evil.