Do better how? Why does anyone think the school is 'cramped'? Because the OP says so? The OP was not a parent, LOL.
I think I am the only person here whose DC has actually been to the school. There is a dedicated rowing facility on the Thames, a dedicated and very large gymnasium building a stone's throw from the main school campus, a dedicated theatre building with bar, seating staging, lighting, several school halls, a ton of classrooms, ample boarding facilities, secret crypts, dedicated common rooms for all of the house, an on-site medical facility with a medical team, several meeting places, two large and secure playgrounds, a dedicated secure playing field (also a stone's throw) with a whole pavilion building, a dedicated music centre with recording studios, umpteen science labs, a huge library featuring an amazing book collection, more than one school dining facility plus on-site coffee shop - all within the confines of Westminster in listed buildings. Plus a mass of accomodation for teachers that means even when public transport has gone to shit, the teachers are still able to teach.
Oh, and all of this is shared with Harris Westminster to ensure that non-fee paying students also get to to participate in A levels in the more niche subjects like History of Art, Classics, Music, Ancient Greek etc.
It is expensive for sure. It is in the heart of London. But it is not 'underfunded', shit nor cramped.