Don't ever disconnect the battery with the engine running!
That can kill a modern alternator.
Make sure that the wiring from the alternator to the battery is good. If it melted the insulating cover on the alternator end, it could have gotten hot enough to have other damage to the insulation on that wire. I would seriously consider replacing that charge wire if possible, but I haven't checked what the battery/charge cables look like on this vehicle and how much that involves.
Have the battery tested again, even if it's new. Have the new replacement alternator tested before leaving the store. If everything tests good, get it all installed and hooked up before starting the car, and don't ever disconnect the battery or the alternator charge wire when the engine is running.
I suspect your original alternator might have been fine initially, and you probably threw away a better alternator than you're going to buy at the stores you're going to.
A battery with a dead cell can overload the alternator and cause the charge wiring to overheat like that, but if the alternator is really strong, it doesn't always damage the alternator.
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I'm not arguing, I'm just explaining why I'm correct.