I would never suggest dripping methylene blue on any fish directly, especially not into an open wound. If you call the company that produces it, they will tell you the same thing. This could be deadly and fast!
Methylene blue is a great med to use for this, but treat the tank as suggested on the bottle, and also add fungus eliminator at the same time (dosing according to directions). The 2 of these medications together will help protect that wound from fungus (which it appears is already growing there) and bacteria.
Yes, keep the tank as clean as possible, and good that you've slowed down the feedings. The fish probably doesn't feel well enough to eat, and it won't starve in just a few days.
As Lupin posted, it's going to be very important for that fish to be out of any medication for at least 24 hrs. The number of medications used in such a short period of time have probably not helped his condition. Each different med induces shock to the fish's system, and some of those meds are pretty harsh.
While this could have started as a heater burn, the continuing deterioration of the wound is quite obviously an infection taking over. Once the infection is gone, the fish should still be able to heal on its own, though I would expect to see some scaring afterwards.
I had a fish who's tank sprung a leak during the night, leaving her to flop on gravel before I found it in the morning. She managed to wear a deep hole into her side from the gravel(as deep as in your photos). I treated with the meds I just suggested and 3 wks later she was fine with just a small scar where the tissue all grew back. If you can kick that infection there is no reason your fish can't heal up the same way... those are the meds to do it!
Really important: don't use salt in the aquarium while treating with fungus eliminator. This med has some salt in it (among other things) and too much of a good thing is no good.
For future reference, never allow a fish to come in direct contact of any med (unless it is meant to coat the food), especially one that is meant to treat the tank water. The potency of the meds would be toxic to any fish that way. When companies bottle these meds, they do it in a concentrated form so that when added to the tank with the proper dose, it is at its proper strength in the water.