I agree, it would be better to show all of the information together. Stay tuned.
A flight builder with dropdowns is on my radar, but I did the text input first for two reasons: (1) it’s faster for me to use since I know the syntax and (2) adding all of the possible options makes the UI quite crowded; text solves the simplest input case and the rest of the information is discoverable / referenceable.
I used a similar syntax to skymilescalculator.com, which I enjoyed prior to writing this but I thought I could have a different take on it.
If you add drop down fields for everything, still leave a manual syntax option!