didn't Solomon make some poor decisions in his later years? and some of the things both did, they did because they were rulers and for political expediency, had to do. this is in itself another reason Christians should beware getting into worldly politics - the Bible never describes the church as if it should wield the sword of the government, in the same way the government should not rule the church. every time it has, it has been a disaster.
but yes i believe he was sincere. it's difficult to come to firm conclusions about his character from history, because what's written about him was written by people who were big fans of his. but we do have the records of the Nicene council, and tho he 'presided' and payed the way of all the representatives to come to it, there's no indication he imposed his will over anything that was decided there.
he did move the Roman empire away from paganism, and even if it was perhaps only in the interest of peace within his empire, he influenced as much of the church that was within the empire to come to terms with its internal disagreements and formally establish what was right doctrine and what was heresy. these were good things. i don't agree he created the RCC - there wasn't any such thing at the time, just one of several bishoprics, of which Jerusalem or Antioch was probably chief, but none of them thought themselves better than the others. all. Christians everywhere were part of the 'catholic' - meaning general - church.
but in fact part of the reason the church in Rome probably started moving towards claiming itself to be head was because Constantine had moved the capital of the empire away from there - so the city that was once great, once the center of power all over Europe and north Africa and the Levant etc, was now hardly important at all. Eventually the Empire would be so busy fighting Islamicists that it couldn't protect insignificant Rome way off to the west anymore, and it was sacked several times. It was in that time period, hundreds of years after Constantine, that the RCC became wholly separated from orthodoxy and divorced itself from the reality of the Bible and of history. They made themselves popes and politically ruled all of Italy because the actual Roman empire had more or less abandoned them.
that orthodoxy that the RCC divided itself from is now what's called the Eastern Orthodox church and has almost not changed at all since that time.