Magnezone hasn't seen a ton of use yet, but you're right to think Choice Specs + Analytic is good on it:
Magnezone @ Choice Specs
Ability: Analytic
Tera Type: Grass
EVs: 120 HP / 252 SpA / 136 Spe
Modest Nature
IVs: 0 Atk
- Thunderbolt
- Flash Cannon
- Volt Switch
- Tera Blast
You can mess with the Speed EVs, but I think this moveset is your best bet when using Magnezone. Tera Blast Grass complements its dual-STAB coverage very nicely, only missing out on Rotom-H, which is taking a lot from your Analytic Thunderbolts anyway.
I've mostly seen Dragon Dance Flygon on hyper offense lately, but Choice Scarf is still a fine set. Its issue right now is an increase in competition for its niches of offensive Ground-type and Choice Scarf user. The latter is really where you see it hurt in my opinion, as we got multiple new Choice Scarf users that are simply faster and stronger than it, such as Mienshao, Infernape, Lycanroc-D, and even Munkidori.