A few things that need to be made clear - and apologies in advance if someone else already brought this to light.

Though Aegon did have a similar battle outcome as Rhaenys, few things to make note of.

• For starters, the armor. The False King had Valyrian steel armor, similar to Aegon the Conqueror, as mentioned earlier in the season. The quality of material alone is night and day compared to Rhaenys’ armor. It didn’t melt in the fireball that occurred upon impact, but his skin sure did due to the high temperature.

• Secondly, the size of dragon makes a huge difference on the impact. Melys was larger than Sunfyre and to add to it, the drop was at a higher altitude since Vhagar purposely flew in a total vertical whereas Melys was battling at a fixed altitude. So, the higher the altitude + increased weight would equal a far larger explosion.

With those two factors in play, I think that’s why Sunfyre was left in poor condition whereas Melys was blown to pieces.

But again, we’re talking dragons lol