the angmo may have set fire to the summer palace in 1860 during the second opium war but it was not totally destroy in the fire. The main cause of the destruction was during and after the 1900 boxer rebellion. With the collapse of Qing power, many chinese, rich and poor, plunder the summer palace of masonery for the building of their own home. Then the final destruction come about during the culture revolution when "working groups" clear lands for planting of crops.
The angmo may start the beginning of destruction but 80% of the destruction come from the chinese own hands. if you want to compare the pictures, then u should see pictures ranging from pre 1860, 1860,1900, 1975 and present. Modern chinese historians admit of 带路党 leading angmo troops to pillage the palace, basically 乘火打劫.