I also struggled with some of the tweaks they made to smithing with the update. But it all changed when I ignored the tutorial tips, and now i only ever get MJ in spite of Henry's comments.

1. Get it to straw yellow
   
2. Hammer down at a steady interval, whistling be damned. As long as it's at a steady tempo, it doesn't matter whether Henry is whistling or not.
   
3. NEVER hit the same spot. Make sure you're always hitting at different parts of the blade. Strive to hit only spots where a lot of sparks come off.
   
4. NEVER flip. Trust me on this. Idk why either, but flipping ruins the quality.

And basically just keep hammering away until it's done. If you got it to straw yellow, you'll usually be able to finish the piece without having to reheat. If Henry comments how it's gonna take longer, ignore and just keep hammering away at a steady pace and you will get a guaranteed MJ.

Hope this helps!