PIC 1
Change
Reaction to Threat = PASSIVE DEFENCE
ROE = ONLY DESIGNATED
altitude = 26,000 ft
See \DCS World OpenBeta\Doc\DCS User Manual EN 2020.pdf pages 276 ff.
Delete "Big Formation" - you don't have one
See \DCS World OpenBeta\Doc\DCS User Manual EN 2020.pdf pages 248 ff.
PIC 4 is an example for 15*3 bombers
It seems that Carpet bombing does not like an altitude above 27,000 ft
If the altitude is 30,000 ft at waypoint 0,1 - the bombers will start a dive from 30,000 to under 27,000 ft at waypoint 1
I set the altitude to 26,000 ft for waypoint 0,1,2 in the edited miz
( about 23,000 - 25,000 ft was realistic over Germany in WW2 - due to the Flak )
( Pretty cold above 20,000 ft - the B-17 has no pressurized cockpit/hull https://meteorologytraining.tpub.com/14269/css/14269_75.htm )
or try this (?)
Waypoint 0 - 30,000 ft
long distance to waypoint 1 for a smooth descent
Waypoint 1 - 26,000 ft
Waypoint 2 - 26,000 ft
Waypoint 3 - 30,000 ft
PIC 2
Waypoint 1
Delete all except Carpet Bombing
Set Carpet Bombing altitude to 26,000 ft
altitude = 26,000 ft
PIC 3
Waypoint 2
altitude = 26,000 ft for level flight over the target between waypoint 1 and 2