Although the Chattan should recite the Berachot, as it’s his Mitzvah to get married and start a family, usually, the Mesader Kiddushin recites the Berachot, so as not to embarrass Chattanim who don’t know how to do it themselves. (Rama and Perisha Even HaEzer 34:1)
Since the Rambam holds that it’s a Birkat HaMitzvah, the Chattan should ideally appoint the Mesader Kiddushin as his messenger to say the Beracha in his place, as it’s his Mitzvah to marry this woman. (Yalkut Yosef, Sova Semachot 6:16)
Rav Meir Mazuz (Bayit Ne’eman vol. 1 Even HaEzer 3:10) asserts that the old Minhag in North Africa and in modern day Djerba was for the Chattan to recite the Berachot himself. Doing so allows Halachic concerns of Beracha Levatalah to be avoided and is certainly possible at any wedding in Israel nowadays.
Rav Eliyahu Ben-Haim in YU does sometimes recommend following the Rambam Kepeshuto also, but he defers when the appointed Mesader Kiddushin is a renowned Talmid Chacham. Giving the Kavod of Birkat Erusin to the Talmid Chacham was more valuable to him.
I heard Rav Eliyahu Bar Shalom elaborate the embarrassment point as follows: the Kallah thinks that her husband is the best guy in the world. It would be demeaning for the chattan in her eyes if he botched this beracha.
Regarding your last point, Shomea KeOneh works as long as one is betorat chuppah vekiddushin, which the Mesader Kiddushin is.
See further in Sdei Chemed (Chattan veKallah 18).