Sondheim is brilliant with his leitmotifs, although they are more subtle. Sweeney Todd, Merrily We Roll Along, Into the Woods etc, are great examples of shows with themes you can spot throughout.
Andrew Lloyd Webber is also a fan of the technique.
It's funny, the three shows you mentioned, Les Miz, Hamilton, and WSS all have an Act 1 closer with multiple themes playing over each other.