Thundurus-T is one of the most viable special sweepers in my opinion. You can run him either scarfed, or life orb. Scarfed Thundurus-T nearly outspeeds everything in the meta except Mienshao, Azelf, Manectric, Aerodactyl, Raikou, and Starmie while they are also scarfed. The only few Pokemon who can really handle Thundurus are Mienshao, getting in a knock off to either cripple scarfurus-t getting rid of the scarf or a stone edge to OHKO, and Aerodactyl with his rock stab. Speedwise those are the only threats Thundurus-T has. Manectric and Raikou are both electric types, and Thundurus-T has Volt absorb nullifying those two. And Azelf doesn't have the power to OHKO Thundurus, and not get OHKOd by a dark pulse.
252 Atk Life Orb Mienshao Stone Edge vs. 4 HP / 0 Def Thundurus-T: 369-437 (123 - 145.6%) --
252 SpA Azelf Psychic vs. 4 HP / 0 SpD Thundurus-T: 172-204 (57.3 - 68%) -- guaranteed 2HKO
252+ Atk Aerodactyl Rock Slide vs. 4 HP / 0 Def Thundurus-T: 312-368 (104 - 122.6%) -- guaranteed OHKO
And LO Thundurus nearly put his sp atk over 500 if not so. And with his movepool he does over half to nearly every sp def in the game.
252 SpA Life Orb Thundurus-T Sludge Wave vs. 252 HP / 252+ SpD Florges: 156-185 (43.3 - 51.3%)
252+ SpA Life Orb Thundurus-T Thunderbolt vs. 252 HP / 252+ SpD Milotic: 283-335 (71.8 - 85%)
252+ SpA Life Orb Thundurus-T Focus Blast vs. 252 HP / 252+ SpD Eviolite Porygon2: 203-239 (54.2 - 63.9%)
The primary counters to LO Thundurus-T although, Rotom-H, Any stalls, since Thundurus-T has no recovery, anything faster than it and has a base stat over 100 in attack or special attack due to how frail Thundurus-T is. 79/70/80 for defenses makes a really fun punching bag.
Last but not least, I did forget this. Priority moves have a lot of an upper hand on Thundurus-T mainly do to how frail he is. Sucker Punch, and Extreme Speed will make the death of him. Making Absol and Honchkrow two of his biggest counters, since Thundurus-T is always seen running hyper offense. Also a Choice Band Arcanine Espeed would do some nice damage.
252+ Atk Absol Sucker Punch vs. 4 HP / 0 Def Thundurus-T: 193-228 (64.3 - 76%) --
252+ Atk Mega Absol Sucker Punch vs. 4 HP / 0 Def Thundurus-T: 214-253 (71.3 - 84.3%) -- (This actually surprised me thought it would be a OHKO)
252+ Atk Life Orb Honchkrow Sucker Punch vs. 4 HP / 0 Def Thundurus-T: 243-289 (81 - 96.3%) --
252+ Atk Choice Band Arcanine Extreme Speed vs. 4 HP / 0 Def Thundurus-T: 171-202 (57 - 67.3%) --