Tano pretty much nailed our thoughts on the harmonies and the arrangement.
And we further agree with the melody note repeats.
I think you were fortunate to connect with such a great vocalist.
And especially one that you could well communicate with.
I rambled on a bit about mastering below. Apologies

Enjoyed it,
J&B
PS There is a post entitled "Loudness Target Limits for Streaming Platforms" on the off topics forum. I responded twice and my second response has some reference to our mastering techniques. You might find the info regarding the use of a "reference song" of some interest. FWIW Mastering for us is very personal regarding what WE want it to achieve. No way could we turn that over to AI. I want control over every aspect of it. You can't make a bad mix sound good with mastering but you can make a good mix sound bad. For us the goal is to make good mix sound great. And you have a good mix.
And if your mastering program is brickwalling the mix it's time to try something else.