I think Scarf Magnezone is trash to be honest, and the only time I'll ever use it is if I'm in need of a trapper + my team is extraordinarily weak to Mega Diancie offense. I think the biggest advantage Magnezone has and half the reason why its Scarf set is even used, is because of its usable bulk, which lets it switch into Diamond Storms, Moonblasts, Outrages, Brave Birds, Stone Edges, and even Draco Meteors if it has to. Yeah sure switching into most of these Pokemon blindly can be bad for Zone because they usually have something to hit it with, but it at least gives your team a bit more defensive synergy in tight situations, and it doesn't force you to always have to find free switch-ins as it can stomach some hits. Magneton is frail as shit, as Latios' Draco Meteor can do upwards of 90% to it, and any of its coverage moves even Surf can either KO it or do comparable damage. Even Mega Diancie is almost 2HKOing it with all of its moves, so it absolutely has to switch into it for free. Even if you look at the most common Scarfers atm, namely Lando-T, Tyranitar, Keldeo, and Jirachi, they all have some sort of defensive utility which makes them useful outside of just pure revenge killing. Magneton is frail as shit, and outside of the few Pokemon it's useful for revenging, it's just really hard to justify using it over a better revenge killer, because I think I'd rather just use Specs Zone + something that can deal with the aftermentioned threats Magneton is meant to revenge. It also kind of sucks that it can't even kill AV Torn-T with T-Bolt after SR, and an un-invested Heat Wave can KO back with just a tiny bit of residual. Most it can do against Zam is break the Sash with Volt but regular Zam is pretty irrelevant anyway and I'd rather just use LO.

The Speed is nice but it's not like we are killing for Talon checks atm, Mega Gyarados is on the steady decline (another Pokemon it can't reliably revenge either), and it can't even reliably check a healthy Torn-T when AV is still very common. Weavile is like the only thing it actually seems to do a decent job at checking, but any smart player is just going to switch out vs Magneton 99% of the time because it's the most obvious Scarf user in the tier. I guess it can move up to C because C- is full of VERY niche Pokemon and Magneton can kind of compress the revenge killer + trapper role into one, but it's still such a subpar Pokemon and Magnezone is usually always going to be the superior option.