On this account I have 6.44 triples per hour with 38 hours played. On another I have 7.07 triples per hour with 56 hours played. I think it has more to do with what heroes you’re playing along with playstyle.
Heroes like Rafaam will generally get more triples, meanwhile Curator has less chance of getting triples since your amalgam won’t be tripled and is always taking up a board space. Some people value keeping doubles over selling something slightly stronger. While some don’t value it and will sell the double for a slightly stronger minion. Some will keep a few pairs and just row for triple while others will sell the doubles soon as they find a slight upgrade etc.
Also with you playing so many hours you most likely played a lot during the amalgam days where you would spend more gold buying buffs rather than like now where we buff a lot less and triple more often.