How do you guys feel the three S rank mons from ORAS PU (Rotom-F, Muk and Stoutland) stack up in today's meta?
I'll go through each Pokemon individually:
Rotom-F: Rotom-F is still solid, however it faces much less usage in the tier for several reasons. First, the large presence of Fighting- and Fire-types in the tier make it difficult for it to thrive in the metagame. In particular, Piloswine, Lanturn, Hariyama and AV Magmortar can switch into its Ice-type STAB pretty easily. Additionally, it faces competition from both Ice-types, such as Jynx and Vanilluxe, as well as by Electric-types such as Oricorio-Pom Pom and Electivire.
Muk: Muk has really fallen from favor in the new metagame, especially with new Poison-types such as Skuntank being extremely prevalant. It did see some usage as a Vivillon answer, however since Vivillon has been banned it's lost its main usage. As
TJ mentioned as well, it's tough to deal with the Ground- and Steel-types in the tier.
Stoutland: Stoutland, while still being good, isn't really up to par with its usage in ORAS. For starters, the introduction of new Normal-types such as Kangaskhan and the reintroduction of Tauros give it competition for its role, although it does have a better matchup against Sableye. In addition, Sand usage seems to be pretty lackluster, although it could see some more usage, especially with Sandslash, Alolan Dugtrio, and Lycanroc.