User blog comment:BannedLagiacrus/Monster Appreciation Week: Barroth (4th Gen)/@comment-36789434-20180910183012/@comment-24734669-20180910191133

So, it seems that Diablos, Teostra, and Kushala Daora have an 88% chance of making it into a game, whereas Rathalos and Rathian have a 100% chance, it seems.

Anyways, I dunno why they managed to come back in World. Perhaps having a beefy mid-tier monster for each biome (well, all except the Coral Highlands) would've been nice, and perhaps Barroth and Uragaan complete the OG Brute Wyvern trio, now that Deviljho's here, I guess?

An equally relevant question would be "Why did Lavasioth come back to World?" It's a boring and/or aggravating fight, it has zero impact on the game whatsoever, and it's incredibly hard to research due to its tendency to not leave many tracks.