Firstly, I would just like to echo what @Shiba said: Dracomancer is outdated and not good to use right now. You will end up losing (a lot) whether you have an optimal stat build or not.
Secondly, to answer your question: Half dragon shapeshift is a bit of a weird skill in general. It costs MP to maintain it every turn, so an investment into INT is advised. 50% of the time it has a melee attack, the other 50% is magic. I'm going to assume two scenarios here:
1). It automatically converts your damage to that type but still respects your weapon stats. Under this scenario, you should already have invested in correct stat
2). The melee attack is based on STR and magic attack on INT. In that scenario, you'd want investment in both STR and INT, so hybrid is the way to go.