The Germans bombed London many times in WW 1 from both airships and heavier than air bombers.
I have a number in my mind from a popular history of the powerful weapons of WW 1 that some of the German bombers could carry about 1000 pounds of bombs, but I have not been able to find a link on Google verifying this memory in my head.
The US Army Air Commands inability to see the future of strategic and naval bombing, pointed out by Billy Mitchell after WW1, was paralleled, later, by that of the Naval Commands inability to believe torpedo bombing would even be possible in Pearl Harbor.
We seem to suffer from a lack of imagination some times. This has been said before in reference to cyber attacks on electric generation and currency values too. The current pandemic has laid bare how effective germ warfare might be against a modern nation.
I found a link stating the Gotha bombers carried about 300-400 Kg of bomb load over London