Oh great... another "bladesmith"... *sighs* ... take a seat.
Protest all you want. The facts remain. Most everything you stated is popular myth and is easily dispelled by a bit of indepth research. My advice to you is to look more to academic / scholarly materials rather then cheap websites maintained by people with zero credentials as the internet is filled with them.
What era of Japanese swordmaking are you refering to? Koto and Shinto are the earliest known periods of Japanese swordmaking, and those blades have a shallow curve but a curve nonetheless. Anything before that is most likely Chinese, or primitive Japanese where no tempering was used at all. So perhaps you're confusing the strength of the blade with the curve when one should be concerned with tempering which incidently, leads to the curve... and more accurately, it is the quenching phase that lends the katana it's curve.
IMPORTANT NOTES ABOUT PRIMITIVE BLADES. Some additional things to consider. Metals used during the primitive era were impure metals. Hence the technique of "folding". You will notice that most straight blades from the primitive era are double edged and are in no way considered Katana.
Onto blade production -
The process of heat treating you are refering to is known to bladesmiths as "Differential Tempering" or "Hardening". Which you have to remember are similiar but different processes in blade production. Curving a blade on the forge -as you say you do- is an amateur technique and not at all considered proper technique. MANY aspiring bladesmiths are taught to do this. I dont.
Anyway, do a little more research before trying to debate someone who has spent years practicing and researching this information. And also, don't lie to me and tell me you're a bladesmith. I would say a hobbyist at best.
Other things you may find offensive -
Japanese swords were not stronger then european swords. The metallurgical sciences during the Feudal period were far more evolved in Italy and Spain then anywhere else in the world.
Blades were never folded "thousands" of times.
Folding the metal to make a blade stronger is no longer required. Uhhh it's called "Metal Refineries". Metal purity and composition is down to a science! Yay for SCIENCE!
If you wish to discuss blade making with actual production level artists go here
www.swordforum.com - also feel free to confirm anything I said here today.
Datus the Grandmaster Ninja assassin. (ninja killer)... (*ahem* i kill ninjas)...