I think my favourite thing about the TATMR soundtrack is the fact that Hummie Mann uses specific musical intervals (how two notes are away from each other) to signal good and evil.
Diesel 10's theme and the other theme i call the Danger Theme are both structured around augmented fourths (which are used in film scoring as a shorthand for danger/death/evil, it is the most dissonant kind of interval we have. The most clashy. You hear one of those and you know smth is Up.
To contrast, Lady's theme is full of perfect fifths (a consonance, open, used typically in film scoring to signify heroes, its the start of Star Wars and Superman for instance), and characters who are good-coded also have lots of those in their themes too
However, the good side also have Major 6ths in their themes too, and this is the interesting part. There's not really anything historically interesting about a major 6th, but the reason it's so prominent in this score is because Mann derives it from the Really Useful Engine song from the show and uses it as a motif - not just for Thomas himself but all the engines and even the concept of being useful - which as we know to an engine (and thus the engine-aligned humans) is equivelant to being a hero.
But why use the Really Useful Engine motif for Thomas? He has a theme, and a famous one at that! It appears only once in the whole of TATMR, when Thomas first appears on screen. Why? I'll tell you why.
Thomas' theme as a really distinct sound, right? The scale up, the fall down. That fall? That iconic sound? It's an augmented fourth.
Mann uses the Really Useful Engine motif to represent Thomas and co. because in the musical language he has constructed for TATMR, if he used Thomas' main theme, Mann would be aligning Thomas with the villains.
And that is just one of the things that tell me this score is really thoughtfully done.