The XT60 connectors are a giant step forward in improvement over the Tamiya connectors. I came across them when my new RC 1/16 scale tank had an XT60 connector on the tank, battery, and charger. Unfortunately, I have a lot of RC tanks/armor, boats, and chargers with the Tamiya connectors installed. Too many to change now, o I made some Tamiya to XT60 adapters.
About the soldering irons, the more expensive ones seems to have a higher quality metal tip on the iron. I see no deterioration at all. The "cheap-O's" tips don't last long and seem to build up a coating that does not transfer heat well unless scraped or cleaned. This possibly could be the problem with melting the insulators on connectors. Food for thought.
Florida , USA
The attached link is the soldering station I had purchased on Amazon. It is no longer available, but this will give you an idea of what I found to be a great soldering problem solver.