Moscow city itself (not the entire oblast) accounted for something like 10% of the entire USSR's industrial output, with a much higher portion of high tech items produced there that weren't produced in any other part of the country. Smashing that (assuming they could in the face of Soviet AAA) would have massive impacts on the Soviet ability to supply the war. That's why the Luftwaffe's Operation Eisenhammer was focused on this region.
RAF bombing of the city center would actually damage to the rail system as well, much as it did to the cities in Germany it carpet bombed.
Soviet night fighters were joke,BUT... england had problem with hitting targets in 1943,too.They would probably must burn entire city to get all those factories.Which was possible for them.In few weeks.