I apologize in advanced, I will be addressing both you and AFD at once, but not going to Quote his post. While it is true that they both have different roles, you still have to compare them, because they are the same mon. You can't have both on the same team, so you try to go for which one is better. I didn't say it was bad because it was choice locked, yet I am trying to say it is limited because of this choice lock. It is true that it does good on volt turn, and that's good, revenge killing is good, but as I said earlier, it can't switch in as easily, to which I will now reply to AFD and you. While Therian does have that good volt absorb, that is it's best bet to switch in, which only does it good against electric teams. While AFD says that it can switch in to electric while not having the 4x weakness to ice, you also have to remember it's defenses. They're the same for both I and T, keep this in mind. 70 in defense, and 80 in special defense. So these are the usage sets for Thundy-T and Mega Manectric, the most common mega on thunder teams (source, the stats)
252 SpA Manectric Hidden Power Ice vs. 4 HP / 0 SpD Thundurus-T: 136-162 (45.3 - 54%) -- 45.3% chance to 2HKO
What Thundy-t's Niche is is the electric immunity, but sometimes, they won't use thunderbolt, sometimes they will use HP ice, which is very common on electric teams. Like, extremely common. Many mons run HP ice every single time. To answer your question, "Exactly how can Incarnate switch in easier than Therian? Therian has that neat Volt Absorb, and they have very similar defenses. I fail to see any situation where Incarnate switches in easier than Therian." Thundurus-I with taunt can switch in on Set-up supporters, like S-Rank Chansey, and taunt it, to render it almost useless. Comepletely without S-toss. Other set-up supporters include Most ferrothorns, all skarms, most hippos, Cradily, Klefki, and so on. The way Thundy-I can switch in that Thundy-T can't, is that it can render the other mon useless, while Thundy-t has to hope to kill, but with eviolite chansey, or usage ferro, that won't happen. Volt absorb is a great ability, that can have it's niche, but with Prankster, it can either paralyze, or taunt with eaze, and be able to leave. It also is a terrific lead, due to it either, as I have stated so many fucking times, it can paralyze sweepers or taunt supports. So there's a turn where you don't have rocks, or a mon that you don't have to worry sweepin your team.
Now, I will say, I agree with thundurus-T being A rank, it is a great mon wen paired, and has to barely adapt. Yet You have to think on this. Which one of these two can you easily slap on any team and make it work? I believe that anttya should add an element of that to the Ranks, how easily can it be put on a team. Alright, I practically made my point, I am going to be reserving Mega Aerodactyl for flying.