Troy showed clear signs that he was just fed up with him being just the leech, which he expressed pretty clear (in my opinion) in the scene where he phaselocks us.
That he was a universal leech and not just on Tyreen made him a possible threat and potentially even able to sustain himself, so there was potential for him living independent.
And the way how absurdly strong he got and how fast he adapted the Phaselock was also pretty impressive. I had somewhat hoped that he would just break up with Tyreen and both went on a race against each other, which would result in the player being part of a hate triangle. Also, there are some echos that portrait him in a nicer and more naive way, which also just wasn’t utilized in the main story.
And last but not least, they could have used a different cliche to their advantage: The “noble” sacrifice! I know I’m reaching here, but Gearbox could’ve have showed Troy becoming unsure about the great vault and about the consequences, which would lead to him doubting the whole plan, getting forced to play along as he is just the leech. In the end he could turn on Tyreen, fully aware that it would mean his death and even help us to stop her, with the final cutscene (or the end credits) showing him on his deathbed, dying a free man.
In general there was a lot of wasted potential and hinted character growth, which unfortunately was barely utilized.