Dave - I disagree to a degree. For both Imperial Japan and Nazi Germany. the prevailing leadership believed the US to weak and soft. Yamamoto was an exception and he was ignored. Speer was an exception and he was ignored.
Even Hitler knew of the industrial capacity and efficiency of American industry to the point of Hitler mentioning Henry Ford in his "Mein Kampf" and Henry Ford being awarded the Grand Cross of the German Eagle.
Several American automakers were involved in German industry (Ford and Opel, for example), there were also alot of other interactions between German and American industrialists.
Likewise, the Japanese were well aware of American industrial potential, as the Japanese and American industrialists interacted a great deal during the 20's and 30's.
Like I mentioned before, the Japanese were banking on the premise that the American public would have no stomach for war and a decisive blow (Pearl Harbor) would demoralize the public and increase the anti-war sentiment. If this didn't work, then a stunning victory of the weakened USN in a grand battle would drive them to the negotiating table.
The problem is, Pearl Harbor had the exact opposite reaction that they were counting on. Additionally, the great showdown never happened. The IJN missed several opportunities to have that "grand battle" when the USN was in a precarious position and time was of the essence, because the U.S. industry kicked into high-gear on a war-wime footing and within a short time, overwhelmed the Japanese. Yamamoto knew this, but I can guarantee you that many others in the cabinet knew it as well, but would never admit it.
The He 162? who thought that up?
Late war desperation...went from napkin sketch to flyingprototype in less than 6 months...
Regarding the Me 262: Since jets were inevitable (the He 178 flew in 1939), the Germans would have been foolish not to develop it as quickly as possible (they started in 1939), and it did make more sense as an interceptor than as a "fast bomber". However, given the stage of jet engine development (Goering cut funding in 1940) and the fact that the Germans were massively outnumbered by 1943-44 anyway, it really makes little difference whether 262's were bombers, fighters, or a mix. Should they have focused on the He 280 instead? Hell no. Just look at the thing. Two jets slung under an airframe that looks more suited to 1939 than 1944. The Me 262 clearly would have had greater potential for development
As far as the He280, it was a fighter in the true sense of the word. According to pilots who flew it, it was responsive, light on the controls and handled remarkabley well. It was well armed, having 3 20mm MG151/20 cannon in the nose, which would have made it one of the heaviest armed fighters for that point in time. A far as having two "jets slung under an airframe"...the configuration of the engine nacelles were not much different than the Me262 and then again, same can be said for the Meteor.
In regards to the He280's timeline historically, it could have been available for production before the Me262's prototype was finished being tested and refined.
So like I've mentioned before, had the RLM had the foresight to embrace and fund the jet program (engines, airframes), the He280 could have been on hand as a fighter AND with the introduction of the Me262 as a heavy fighter (interceptor), it could have flown top cover and protected the Me262s as it attacked the bombers (the bombers were inevitable...there is no way Germany would escape that).
The only difference historically, is that if Germany had gone ahead with the jets early on, then Britain and the U.S. would have ramped up their programs as a priority (the P-59 first flew in 1942) and the air battles over Europe would have had a much different look.