The Yer-2s have their full payload, but the B-17s and Avro Lancaster don't.
There are endless posts about the payloads, short version: B-17 could carry up to 16,000 pounds of bombs, the Avro Lancaster fourteen 1000 pound bombs or the 22,000 pound "Grand Slam"
In a few of the Q&As, people talked about that: http://forum.warthun...us-transcripts/
Q: Yer-2 and why it carries more bombs then any other bomber in game?
A: Have to be checked with developers, not sure.
Q: Bomb load of some bombers in the game is lower than what bombers could take in real life?
A: That was done intentionally because of balance and necessity to stop bombers from killing all ground units in one pass.
Will we see a bigger bomb than 4,000 pounds?
Borisych: Yes! We will have bigger bomb loads available.