The Lancaster was a contemporary of the B17.
Indeed, although designed for different tasks. But in your previous post, you stated that the Lanc and B-29 were contemporaries, which is somewhat misleading!
The B29 could be developed as the US had both need and capacity.
We certainly had the need for an advanced aircraft design, and the capacity to build them! What we lacked though was the technical skill. Had we been able to develop an aircraft as modern as the B-29, Bomber Command's losses would have been significantly lower. Instead the brave men of Bomber Command had to make do with decidedly 'old tech' aircraft like the Lanc and Halifax, and paid dearly for it.