As stated, B-17s, B-24s, B-26s and Ki-67s are not free kills, but they are individually very easy kills. Haven't tangled with Tu-2Ss so I can't comment on them.
You are also reading too little into simple K/D ratios. You're simplifying what it means to make a point. Spitfires, A6Ms, N1Ks, Hurris, Ki-43s and the Brewster are often used as last ditch defense fighters taking off from vulched, or nearly vulched, air fields. That very significantly reduces their K/D ratios. P-40s just suck so I am not even sure why you mentioned them as their K/D is obviously going to be sub par.
What none of you guys have explained is why you think that bombers would even be used if formations were removed. The best of all free bombers, air-to-air wise, has an effective K/D of 1.17 with formations. Take away formations and you remove two thirds of its sortie durability and a significant chunk of firepower as well as cutting its payload from 18,000lbs to 6,000lbs. With that change you would drastically reduce its effectiveness and probably drop its K/D ratio to no better than .25 to 1, quite possibly less.
So, why would somebody plan to spend one or more hours trying to get that to target when they could easily make four or more P-51D suicide runs in the same time and be more likely to actually get their bombs and rockets to the target? What motivation would you provide to make the bombers anything other than nearly extinct curiosities that people try once in a while only to realize why they aren't used and go back to their kamikaze heavy fighters?
You spend a lot of time talking about how it isn't fair that the bomber hurt you, but no time at all talking about what happens after the bombers get gutted to make them suicide rides.