"It stands to reason that trains are large and heavy, whilst leaves are small and light, so leaves can’t stop a train."
"It stands to reason that trains have solid metal wheels, so trains can’t get ‘flat tyres.’"
Well, you might think so, but you'd be wrong (though since tube train wheels don't actually have tyres, you'd be strictly speaking right about the second point).
For a highly detailed discussion of the problems afflicting the Piccadilly Line since Storm Angus passed over London on 20th November, head over to London Reconnections. (If you have trouble getting to sleep, I recommend starting to go through the 104 comments by readers, starting with the one written by "Pedantic of Purley".)