If you want a blade that is twice as thick then you have to create a pile of metal filings which is 4 times bigger. This why I like making small knives. Hot sawing' involves using a dull power jigsaw blade, no lubricant, high speed and lots of pressure. After everything heats up and the sparks fly it will cut very quickly but not give a super smooth edge. The freshly cut edge of the blade will actually be hardened by the transient heating that accompanies the cutting.
Hard steel is the sort of thing that ruins files.
Consequently you will need to remove the thin hardened layer with a grinder before you do any filing. If you had infinite patience and dexterity you could hold the knife blank in one hand and the file in the other while you shaped the blade. That would probably be the last knife you ever made. Good ergonomics requires clamping the knife blank at waist height so that you can apply your body weight and muscle power to the file in order to make the bevel quickly, accurately and neatly. Use both hands and apply a very great pressure to the file.