He’s naturally more submissive by design, but there will gradually be more dominant scenes as the story progresses. It's not really necessary to lower his submission stat. Fetish stats only influence resistance chances during quickrolls and will start affecting combat abilities in 0.7. They don’t decide which scenes you’ll get, though. Those are controlled by different internal variables that you can track in the "Special Values" section of the diary menu.
You can actually build both dominant and submissive traits at the same time. There are a few scenes that raise dominance too (just fewer compared to the submissive ones of course).
As for his personality. He's not the type to willingly cheat on Liora at this stage. Most other characters will be the ones trying to seduce or corrupt him. Over time, as he gains more experience (whether through Liora or others), he'll start acting more willingly and with that, become more assertive.
This approach for scenes is also needed so players aren't forced into content they're uncomfortable with. Someone who only plays gay content or only straight content will naturally end up with fewer fetish values than someone who plays everything.
Here's a screenshot from one of my test runs after a full playthrough, dominance reached level 34 by the end, which is pretty high.
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