Throh/Nageki's stat distribution actually looks really good. 100 attack is just enough for it to inflict damage on things it needs to, and thanks to good coverage (Payback, fighting type attacks, Stone Edge/Rockslide, Earthquake), it can always pose a threat.
It's defenses are great, the immediate defenses it has are even better than Reuniclus (but Throh lacks any immediate recovery or magic guard), and despite not having a means of immediate recovery, it's unwise to inflict status on it right away due to Guts. Giving Throh a 1.5x boost to all of it's attacks is a pretty steep price to pay for residual damage.
If Throh packs Revenge, it's got an immediate 120 BP move before STAB without sacrificing attack or bulk, like it would if it used Superpower. Throh's HP and defenses allow it to use Revenge rather effectively as well, but again, residual damage is problematic for Throh since it has no reliable recovery options, and leftovers will probably be it's best bet.
Throh can also safely deal with ghost types thanks to it's access to Payback and again, it's good defenses. While healthy, Throh can survive nearly anything that's not supereffective. Pokemon like Chandelure also won't enjoy eating Stone Edges or Rockslides (or Earthquake) and should you want, Throh can also go for stat reducing moves like Ankle Sweep or Rock Tomb to pester with opponents as they try to work around it.
Throh basically stops Tyranitar cold as well, as it fears nothing from Tyranitar, and can easily OHKO it with it's STAB moves. Fighting is a very solid defensive type, as only Flying and Psychic type attacks will give it trouble, and neither are very common attack types. However, it is unfortunate to be weak to flying, thanks to the prevalence of Skarmory, which can switch in on Throh and shrug off virtually anything it can throw at it, and phaze it away. Worse yet, Skarmory can just as easily hit a high powered Brave Bird into Throh. Even with investments, surviving a 360 BP move (120 x 2 x 1.5) is a rather tall order for Throh to fill.
Throh makes an excellent partner for the aforementioned Reuniclus too. Throh has no issue with switching into oncoming dark type attacks (though the most common dark type attack, Pursuit, makes it kind of annoying to switch in to), and Reuniclus can cover Psychic type attacks aimed at Throh. Reuniclus' ability to set up Trick Room also compliments Throh's terrible speed, making it one of the quicker trick room users.
Throh's main issue is competition with Conkeldurr. While Throh obviously sports more balanced defenses, Conkeldurr has a massive 140 base attack (which is better to abuse guts with), the same speed plus an option to use priority, and even a recovery option. In order to not be outclassed, Throh should focus on trying to use it's phazing capabilities along with it's good mixed defenses.