Nothing is unhealthy about belting. Around the 70's there was definitely an uprising of more rock-ish "screlting" in JCS and Hair, etc, but that trope has gone away recently in favour of a more clean, contemporary, mix-y sound. If you're trained correctly and practice safe technique, you won't damage your voice, and that same principle applies whether you're singing in a high belt, as a lyric baritone, or in a character voice. I don't know why you think it's unattainable for most performers - that simply isn't true, and you only have to look at the people coming out of the top MT schools to see that it's achievable and sustainable even with only very few years of training. There are also very few things that match the thrill of hearing/performing a solid, clean, high, belt note.

As far as melody goes, I think it depends on what you mean by "better" - I'd agree that Rodgers' melodies are consistently some of the most beautiful, but part of that is due to the style/what musical theatre was perceived as back then. Much like in modern pop, songs from that era were allowed to indulge in themselves more, at the cost of consise and clear story-telling; the lyrics were (generally) perceived as less important and characters would constantly go on poetic tangents that existed for the sake of being poetic and pretty, not for advancing the plot. We see less of that now, because music theatre has advanced to be a lot more story-based. IMO a "better" melody is something that expresses and compliments the lyrics clearly to the audience so that they fully understand the meaning on their first listen, like in Sondheim, Cy Coleman/David Zippel or Lin-Manuel Miranda's work.

Ahren's and Flaherty are great - I think because Anastasia is their most popular work currently and IMO not one of their best, they don't get as good a reputation as they deserve.