I'm still going to say that that that dent can be mostly popped back out with some hardwood tube clamp blocks, a bench vise, and some elbow grease.
You clamp the tube over the dent, tighten the vise until you feel a decent amount of resistance, rotate the tube in the blocks by pushing/pulling the frame's downtube, tighten some more, rotate, etc. until the clamp blocks are completely bottomed out on the tube surface. The pressure on the high spots around the dent will force the tube wall to pop back out where it was indented.