Thing From Below is simply stronger than both those things, by a large margin. It's perhaps the only busted card in the game atm in terms of power level. So yeah, nothing close.
Dragonfire potion is amazing, til you realize it can only be fully utilized in a dragon priest deck and then it doesn't even scratch one of the most popular 5 drops, azure drake. It's probably a dead card vs any dragon deck, including dragon warrior. I also think it's weaker than light bomb. Yeah, it's still a good card despite all that, but we're talking about TFB strong.
Then the 5 drop dragon? That requires you to have a dragon in hand? It's a glorified thoughtsteal. It's slower than ethereal peddler, because with ethereal peddler you can actually play 2 mana cards you've reduced on that turn, or make busted plays the next turn. Despite that, it's still a good card that will see play in dragon priest. Mainly because azure drake is rather mediocre in dragon priest. It's not TFB busted strong, is what I am getting at again.