I don't really see the extent and reach of the curriculum as "narrow", to be honest. A quote from their book:
How, then, are we to decide which knowledge to teach? At Michaela, we decide based on challenge and coherence. We prioritise the core academic and artistic subjects that help pupils understand the world and live fulfilling lives: Maths, English, Science, History, Geography, Religion, French, Art and Music. The subject knowledge we choose to teach our pupils to master is the most vital and the most challenging content. The pupils we teach often arrive at school far behind, unable to read fluently or multiply. Many have a vocabulary of fewer than 6,000 words, while wealthier pupils often have one of over 12,000 words. The opportunity cost of teaching anything other than the most challenging subject content is high. Only the most challenging topics with the most stretching vocabulary, combined with high support so all pupils understand and use it accurately, will allow them to compete academically with the 96% of private school pupils who reach university. We dedicate extended teaching time for the mastery of grammar, spelling and vocabulary; these are the hidden bodies of knowledge that make for accurate writing. Our pupils already have vivid memories of reading some of the most complex and beautiful texts ever written: Shakespeare’s Julius Caesar, Swift’s Gulliver’s Travels, Shelley’s Frankenstein, Orwell’s 1984, Malcolm X’s autobiography, Maya Angelou’s autobiography, Duffy’s The World’s Wife and Mandela’s A Long Walk to Freedom, to name just a handful of examples. Our aim is to help pupils remember everything they are learning, and master the most important content.
To this end, subject content knowledge is best organised into the most memorable schemata. So we organise History and English Literature chronologically. We start in year 7 with classical antiquity: in History we study Mesopotamia, Egypt, Greece, Rome and Roman Britain; in Religion, we study polytheism, The Old and New Testament, Judaism and Christianity; in English, we study Homer’s Odyssey, Sophocles’ Antigone, Aeschylus’ Agamemnon, Euripides’ Medea, Cicero’s rhetoric, Seneca’s stoicism and Shakespeare’s Julius Caesar; in Art, we study Egyptian, Greek and Roman art, sculpture and architecture. Chronological, cumulative schemata help pupils remember subject knowledge in the long term, not for ten weeks or ten months, but for ten years and beyond. ... At Michaela, our pupils remember year 7 as the year they learnt about Classical Civilisation. Across subjects, they are making exciting connections. Sacrifice, for instance, recurs in the stories of Abraham and Isaac in religion, with Agamemnon and Iphigenia, and Minos and Theseus in Greek mythology. Across English and Science, the planet Mercury is named after the Greco-Roman messenger god, as it is the fastest-moving planet that takes 88 days to orbit the sun. A dovetailed knowledge curriculum allows pupils to make limitless fascinating connections for themselves, and understand the ideas of democracy, dictatorship, tragedy, monotheism, sculpture, geometry and algebra from their early origins. In short, we select challenging, sequenced, coherent schemata within and across subjects, so that our pupils remember what they’ve learned for years to come.
And no, they don't teach geography GCSE, but geography is taught in Years 7-9 as part of History.