Sounds like you’re pretty close to getting it. Keep going! I encourage you to read more writing by trans people, especially more narratives about our self-discovery and self-acceptance journeys.
You’re right that gender norms don’t make sense. Most of them are totally arbitrary, confining, and stupid! And you’re also right that gender roles do not define who we are. I’m not trans because I’m too “masculine” to be a woman. I’m actually not masculine at all. I’m an effeminate man, or something close to that. So it’s not the case that someone just crosses a line of masculinity or femininity and then “becomes” that other gender. Lots of trans people are themselves gender non-conforming.
There are butch trans women, feminine trans women, masculine trans men, every possible combination imaginable, just as there is with cis people. Identity isn’t tied to how sterotypically masculine or feminine we are, anymore than it’s tied to our genetics. Gender encompasses a lot of stuff beyond gender norms and roles — which groups we feel safe with, who we identity with and look up to, how we feel about our bodies, how we experience attraction, how we dress, how we move, how we see ourselves. It’s a messy tangle. Keep searching and reading and trying to learn more. It’s so much more complex than just biology and adherence to silly social rules.