How do third party ones work without this melting issue I wonder?
By not having Apple Watch support. The Watch uses smaller coils, hence why the Watch charger is much smaller than the Magsafe charger.
So they tried putting in coils that overlap other coils hoping that they can service both Qi coils on the iPhone and AirPods case while also supporting the Apple Watch coils. But the problem is when you’re not close enough coil-to-coil between charger and device, most of the energy turns to heat instead of electricity. The heat builds up and gets hotter the more charging is done. The only way this can work out is if you charged in freezing temperatures because then it would cool down the charger and phone quite rapidly.
Or the realistic alternative was to put a fan and gel cooling in so the coils could all be cooled, but Apple didn’t want to put a fan in, not their style. As a result, Magsafe was created which relies on close positioning from coil to coil. And similarly, the other chargers that do this support Qi but not Apple Watch charging. Also they probably have some better cooling, they’re usually like 1 inch thick and probably have some extra copper tubes or gel cooling.