Two things to think about, V. - first, the bleeder bolts. Experience has taught me that if you open the bleeders more than a fraction of a turn, they will let air in. Seems you addressed that with the teflon tape, but creating too much vacuum may be overcoming the tape. I've noticed the air problem can be significant when not applying any vacuum over that caused by the return stroke of the master cylinder.
A slight amount of sponginess will usually disappear with use as the bumps and repeated brake use allow the air to make it to the reservoir and be replaced in the lines by fluid.
I would avoid using the teflon tape on a bolt which must be loosened and retightened. Its good for something like the fan switch, but considering the possibility of a piece of tape breaking off when the bolt is loosened and tightened again,and working its way up to the m/c and possibly clogging a pressure relief orifice makes me apprehensive.
Over the years, I've noticed four issues that affect brake feel & performance:
1) The accumulation of brake dust and dirt around the exposed circumference of the caliper pistons. Whenever I change pads, and sometimes more often depending on what I see, I take a toothbrush, cloth, and brake cleaner and remove all dirt from around the pistons. I do this by forcing each piston in turn ALMOST completely out of its cylinder. When you can rotate each piston by hand, it is out far enough. Make sure it is clean completely around its circumference. If this has never been done before, you will notice a fair amount of corrosion on the piston. If the corrosion is too bad, the caliper will never feel like new, no matter what else you do.
2) Burrs, raised edges or deep indentations on the rod which guides/supports the brake pads.
Cleaning and a few strokes with a points file will keep your brakes feeling good for the life of this rod. Good cleaning keeps this rod in the game for about 40k miles replace after that or when the indentations become too deep.
3) Pad contamination. The pads can be contaminated from any number of fluids, including things thrown up from the road. Replacement is the best option.
4) Old fluid. You being you, I'm certain this doesn't happen on your bike.
Gallons of fluid through the system? I've read your posts for years, and I have no doubts about your mechanical proficiency. In this case, I feel there may be a flaw in your bleeding process. I'm sure you'll get to the bottom of it.
I've never had to replace a m/c, and I've replaced one caliper on all of the 11 bikes I've owned. This with ~ 1 million total miles. It is from this I arrived at the knowledge I write here, not from any special brake knowledge or training.
You'll figure out a better way to remove air from your brakes, that's just the way you roll!....