The attached paper is an interesting comparison of the capabilities of the Halifax vs the Lancaster
An interesting read with lots of useful detail. It pretty much confirms what I said earlier about the Halifax. It doesn't delve into why the Hali had so many airframe deficiencies when it first appeared though, the author preferring to brush over them by saying he doesn't know. To be fair, the answer is a difficult one to quantify, but HP and its designers were tackling their first all-metal four-engined heavy bomber and at the time it was a difficult thing to get right ( something people don't really take into consideration when reflecting on the time period before the war) and few manufacturers around the world were actually building big complex four-engined bomber aircraft for series production, prior to WW2 (Focke-Wulf - an airliner, so doesn't really count, Junkers, Boeing, Douglas, HP and Short Brothers to name a few of the most notable).
The HP.57 was an entirely new design, rather than an extrapolation of work done on the HP.56, which only appeared in drawing form, so to create the Halifax the aircraft was entirely redesigned on paper first - the two had virtually nothing in common, apart from similar looks and obvious lineage, so the statement about difficulties arising from its conversion from a twin-engine design doesn't really stand.
Volkert over-complicated several aspects of the Halifaxes' design; its bomb bay doors for example were in eight pieces, the lowermost retracting
into the bomb bay, which restricted the ability to carry big bombs because of the location of the door actuators and the space required to store the doors, and the addition of Boulton Paul turrets, which were heavier than the Nash & Thompson ones on the Manchester added weight. This was despite being a more advanced design than the N&T ones, having their own power generation and hydraulic systems separate from the aircraft's - if the aircraft hydraulic system fails, the turrets are still useable - easier to use as well, a single joystick, leaving one hand free to deal with cocking and jamming guns - N&T turrets required both hands for operation.
These are but two things behind the Halifax that contributed to airframe deficiencies, but what the Halifax and Short Stirling do is illustrate the issue of weight creep in a design. Both Britain's first four-engined heavies suffered in that respect; both were overweight, which affected their performance and load-carrying capability. This came about from various things, the operator changing specifications mid-design doesn't help etc... Both also introduced complex electrical and hydraulic systems, the architecture of which within an aircraft design is a difficult thing to incorporate, especially if beginning with never having designed them before - the Manchester was the same, very advanced system-wise for the time, especially since the first all-metal advanced aircraft Avro had built before the Manchester was the Bristol Blenheim under licence. Its own contribution was the Anson, which even by 1936 was dated.
Then there were issues with the engines, which overheated - its radiators were inefficient, requiring input from Rolls-Royce... The list goes on...