Them thar is fighting words Smokey
When making claims like that it is best to have all your ducks in a row and unfortunately your ducks are different breeds in different ponds.
Crash of prototype had nothing to do with the qualities of the aircraft, good or bad. They tried to take off without unlocking the control surfaces. Gust locks had been installed to keep the large control surfaces from flapping around in the wind and getting damaged. One thing that came of this accident was take-off check lists. Douglas got the contract, in large part, because a twin engine bomber was cheaper than a 4 engine. They could get a lot more planes for the money ( first order for B-18s was a whopping 82 aircraft)
The 4000lb bomb load is a furphy that just will not go away. It seems to have got it's start in an offhand quote from a General to a war correspondent. B-17s routinely carried 5000lb loads to Berlin and 6000lbs on occasion to Berlin and often on shorter flights. The element of truth to the 4000lb load is that while the Berlin bound B-17s carried 5000lbs of iron bombs the ones carrying incendiaries carried a bit over 3000lbs so the average was 4000lbs.
A B-17, with the external bomb racks (seldom used) could get 17,000lbs off the ground, it just couldn't go very far with it.

External racks would hold a pair of 4000lb bombs (or smaller) and did not block the bomb bay.
Mosquitoes could not carry the 4000lb cookie until 1944 so what they could or could not carry makes little difference to B-17s in action in 1942/43. Mosquitoes carried four 500lbs inside and two outside at best for the first year or more of operation. And they very rarely carried incendiaries except for target marking.
The British "test" was flawed for a bunch of reasons. Despite being told that the B-17Cs they got weren't really ready for combat the British used them anyway, in the typical British "penny packet" numbers, rarely more than 3 aircraft per mission, which is hardly enough to set up the defensive formation quantity of fire the 'theory' depended on. The as fitted armament consisted of a single manually operated .50 cal out each waist window, one, 50 cal out the back of a ventral tub and the fourth out the top of the radio compartment, however field of fire and indeed field of view for the dorsal gunner were best described as restricted.
View attachment 483890
There was one additional .30 cal or .50 cal in the nose. British were using either two or three power turrets in most of their bombers at this point and why they thought that a handful of manually aimed .50 cal guns was such a big improvement as to allow daylight operation is beyond me.
The B-17E was already on order when the RAF got their 20 Fortress MK Is and with double the number of guns and twin dorsal and ventral power turrets the firepower was significantly higher. Still not enough as it turned out but there was reason to discount earlier experience.
BTW you might want to check on that just a few more bombs a little bit further for the B-29 comparison also.
Ok, sorry it's a bit late i had to dig out my files from the loft/attic.
Bombs: Although it theoretically could carry 17,417 lb of bombs, the B-17 rarely flew combat missions with more than 5,071lbs to 6,000lbs. This was because of its poor climb rate with load, poor performance at altitude and the low power to weight ratio of the Wright cyclones. (Although i have a feeling you will try and debate that)
12,732 B-17's were produced at a cost of $238,329 each. Today, the same aircraft would cost $2,781,367 apiece. That's a hefty price tag for a 1935 design. Not to mention most of them went down in flames.
Because of all the guns, which were basically redundant, it had a ten man crew. That's ten guys every time one went down. Admittedly a few managed to bail out but effectively for them the war was over. It was used wrong, despite the RAF's warnings thousands of young men were needlessly sacrificed on what was suicide missions. Without the P-51 the whole planes history would have been a disaster not a triumph as some seem to think. The Norden bombsight was nowhere near as accurate as claimed and time and again crews were sent out to bomb the same location day after day. The suits worn were totally inadequate and led to many deaths by asphyxiation and even electrocution. Also the B-17 was not a heavy bomber just because it had four engines. If anything it was a mediocre medium bomber.
Losses
These statistics came from the 398th BG newsletter. These numbers match up with what I have seen listed by individual unit histories and in reference books. It also matches up with the wall in front of the American Air Museum before the unit names were worn away by rain.
Bomb Group Station Bomber
Type Missions
Flown Losses First number denotes amount of aircraft. Second number losses.
34th Mendelsham B-17 170/ 34
91 Bassingbourn B-17 340 /197
92 Podington B-17 308 /154
94 Bury St. Edmonds B-17 324 /153
95 Horham B-17 320 /157
96 Snetterton Heath B-17 321 /189
100 Thorpe Abbots B-17 306/ 177
303 Moleworth B-17 364 /165
305 Chelveston B-17 337 /154
306 Thurieigh B-17 342 /171
351 Polebrook B-17 311/ 124
379 Kimbolton B-17 330/ 141
381 Ridgewell B-17 296 /117
384 Grafton Underwood B-17 314 /159
385 Great Ashfield B-17 296 /129
388 Knettishall B-17 306 /142
390 Framlingham B-17 300/ 144
398 Nuthampstead B-17 195 /58
401 Deenthrope B-17 256 /95
447 Rattlesden B-17 257/ 97
452 Deopham Green B-17 250/ 110
457 Glatton B-17 237 /83
486 Sudbury B-17 188 /33
487 Lavenham B-17 185 /48
490 Eye B-17 158 /40
493 Deebach B-17 158 /41
Total 10631 /
4145
Almost half of the amount of aircraft on each mission failed to return