Yes, it’s true there are probably more soprano roles, but actually, there are many lead mezzo roles - Not just Carmen. Almost all of Rossini’s heroines were written for mezzo. I sing many of those arias. Many of Donizetti’s roles and roles created during the early 1800s were actually for a mezzo, but for some reason the soprano took them over. Richard Strauss wrote gorgeous parts for the mezzo which equal with the sopranos. You also have Handel which can be sung by mezzos or sopranos. Mezzos, especially lyric mezzos like me, can also switch up, so they have a slightly larger repertoire.
I don’t believe that is true. Having sung in both volunteer and professional choirs, directors always talk about problems of trying to find more altos to sing. I always had to switch singing alto or soprano if they didn’t have enough altos.
I don’t mean this in any lack of respect, but do you work in the opera world and are you an opera singer? I’m a professional opera singer and have sung and studied here in the states and in Europe. I believe I have some expertise in this. I know that it is truth. There aren’t as many mezzos or altos in the world, so it is a lot easier for a mezzo than a soprano to get a part. It’s still a very tough road to haul, but in terms of competition, it isn’t as difficult. Also, as I explained, if you perform in the opera world, you would know that 99.9% of arias are not just for sopranos. I wouldn’t have so much repertoire if that was truly the case.
But I think we’re going off topic. Again, the soprano range is above the range of what is written in the hymns. The range in hymnody is always in the middle or lower voice - never in the soprano range. A typical alto range is from low F to the E, so even if you don’t believe that most women are sopranos the music isn’t written in the soprano range anyway.
And please, I hope I’m not sounding like I’m arguing or being rude. I don’t mean to be. Here’s my smiley face to prove it.

God bless.
P.S. I didn’t mean that mediocre mezzos could get the jobs. A mezzo still needs to be darn good. I only meant that for tenors. There are more mezzos than there are tenors, so mediocre tenors can them much easier than mezzos. Sorry I didn’t make myself more clear on that.