I'm not opposed to Machop moving up. I hate how a large portion of its effectiveness relies on hax, but at the same time having used it more than I used to I can't deny that it's more useful than a significant amount of the stuff in D.
Hax should not be the entirety of an argument against a mon moving up. While it's certainly something that should be taken into account due to not being entirely reliable, if the luck-based part of the Pokemon has no real downsides then there's not much of a reason to use that as an argument against it. For Machop, Dynamic Punch confusion is not something to be held against it in terms of viability, although it's certainly something to complain about if your opponent brings it.
Machop as a scarfer has several important things going for it. First is, of course, Dynamic Punch. The confusion that this move brings with it means that checks and counters have to be significantly safer than usual, as a Pokemon that is 2HKOed but can OHKO back has a 50% chance to fail in checking Machop. This also helps Machop's not terrible bulk, even with a choice scarf. When spamming its STAB Machop is just statistically less likely to be hit by an attack, making its bulk better than the numbers, similar to how Regenerator gives Mienfoo greater bulk than it seems. This amount isn't nearly as much as Regenerator, but it helps.
A second thing going for Machop is its interesting coverage options. Like almost every Fighting-type Machop does get Knock Off, but it also has access to Earthquake, Ice Punch, and Poison Jab. Rock Slide is another option, but I'm not personally a fan of it. While being locked into Earthquake or Ice Punch isn't great, what these moves offer is a way to prevent most Poison-types and Ponyta from countering Machop. This in turn means that Machop has fewer things able to switch into Dynamic Punch without getting nailed by coverage.
Is Machop a great Pokemon? No, but while it has does have some reliance on hax to be as (or arguably more) effective than things like Scarf Mienfoo and lacks pivoting it's still effective overall.
All that being said though, I think it's more a D rank Pokemon than C-. I can just see it as a potential low C- Pokemon.
Mankey's more effective than you're giving credit for though Reuniclause.
Hax should not be the entirety of an argument against a mon moving up. While it's certainly something that should be taken into account due to not being entirely reliable, if the luck-based part of the Pokemon has no real downsides then there's not much of a reason to use that as an argument against it. For Machop, Dynamic Punch confusion is not something to be held against it in terms of viability, although it's certainly something to complain about if your opponent brings it.
Machop as a scarfer has several important things going for it. First is, of course, Dynamic Punch. The confusion that this move brings with it means that checks and counters have to be significantly safer than usual, as a Pokemon that is 2HKOed but can OHKO back has a 50% chance to fail in checking Machop. This also helps Machop's not terrible bulk, even with a choice scarf. When spamming its STAB Machop is just statistically less likely to be hit by an attack, making its bulk better than the numbers, similar to how Regenerator gives Mienfoo greater bulk than it seems. This amount isn't nearly as much as Regenerator, but it helps.
A second thing going for Machop is its interesting coverage options. Like almost every Fighting-type Machop does get Knock Off, but it also has access to Earthquake, Ice Punch, and Poison Jab. Rock Slide is another option, but I'm not personally a fan of it. While being locked into Earthquake or Ice Punch isn't great, what these moves offer is a way to prevent most Poison-types and Ponyta from countering Machop. This in turn means that Machop has fewer things able to switch into Dynamic Punch without getting nailed by coverage.
Is Machop a great Pokemon? No, but while it has does have some reliance on hax to be as (or arguably more) effective than things like Scarf Mienfoo and lacks pivoting it's still effective overall.
All that being said though, I think it's more a D rank Pokemon than C-. I can just see it as a potential low C- Pokemon.
Mankey's more effective than you're giving credit for though Reuniclause.