This claim seems to be coming from a person who has no basic knowledge about Quran, or a person who has not read the whole Quranic verses.
1. Quran has many verses of prayers to Allah in which Allah is teaching us how to supplicate and what are the best words of supplications. These verses which are found in many Suras including Sura Al-Fatiha never mean that Allah is addressing Himself, but He is teaching us the best way and wordings of supplications. Books were compiled on the Quranic verses of supplications.
2. Quranic Suras starting with 'Say' are just five out of 114 Sura ( Al-Jinn, Al-Kafiroon, Al-Tawheed, Al-Falaq and Annaas). There is no question and no reason at all to claim that al-Fatiha should start with 'Say'
3. There are five Suras in Quran starting with the supplication word; Alhamdulillah الحمد لله ( Al-Fatiha, Al-An'aam, Al-Kahf, Saba', and Faatir). Non of theses Suras started with 'Say'
4. Sura Al-Fatiha or Al-Hamd is the greatest Sura in Quran according authentic Hadeeth. It is called also Ummul Kitaab 'the mother of the book' and no Salah can be prayed with out reciting it " There is no Prayer with out Fatiha لا صلاة إلا بفاتحة الكتاب