Your citing Eaker's replacement by Doolittle was suggestive that Eaker was relieved due to an error in judgement regarding enemy flak attributes and that changes were effected after his replacement (re: altitude). Neither was the case from what i have read. Platform limitations were one of the factors that helped determine USAAF altitude settings but not the only one.
I have heard repeatedly, by several individuals at a command level that their opinion bears weight, that Eaker was deemed to have failed to achieve the objectives necessary to make the case for US daylight strategic bombing - and the decision was made in the October timeframe.
In these discussions Eaker and Spaatz and Arnold were at odds regarding which changes in current strategy were required to a.) stop the bleeding and b.) win air superiority for the upcoming invasion.
The cornerstones of the debate were a.) switch to night bombing as requested by Churchill with a somewhat receptive audience in FDR, b.) violent disagreement from Eaker and Arnold for reasons ranging from training to equipment to logistics of cramming USAAF and RAF over UK in 10 hour window to perceieved ineffectiveness against both Luftwaffe and strategic targets.
From what I heard Eaker offered no real solutions and was not convinced that long range escort was the answer - as well as adamantly opposed to fighters ranging away from close escort.
Doolittle was a candidate for the 8th AF job but Eaker was well respected. The decision came down to Spaatz accepting the responsibilty for both the selection and the results of a new commander but USAAF Strategic Bombing doctrine was on the line and so was Spaatz's job.
The 8th conserved strength in late Oct through early January as the P-38 and then P-51 were evaluated for long range target capability... The reviews from Tommy Hitchcock who headed up 8th A technical evaluation were so glowing that the die was cast and the 354th FG was TDY from 9th AF to 8th and deals were cut to transfer 357FG to 8th in exchange for 358FG (jugs), as well as transfer all P-38s and P-47s to 9th AF TAC as all future deliveries for the P-51 were switched from 9th to 8th.
The die was cast in approximately November 1943 even before the first 354th FG mission was flown.. A HUGE gamble.
Flak effectiveness had nothing to do with the decision - it was all about killing the Luftwaffe as fast as possible and accept whatever casualties required by 8th BC to get the job done.
Doolittle made the command decision as new 8th AF CO and the infamous memo to 'seek the enemy in the air and on the ground' was one of his first, and early, directives.. I think January 11 but my memory is poor and I am away from my references. Many 8th BC Group Commander privately called Doolittle a 'murderer' for his decision to free up the escort as they envisioned a slaughter..