I disagree. For me it's just like what that guy observed. Actually, it seems that the pattern goes like this;
Overlord - "Child" (like Sid was referring them) Rider - Adult Rider.
The Overlord seems to have some of the attributes of the "Child" Rider and some of the Adult Rider, but some unique characteristics, while the Riders differ quite a lot too.
For example;
Roshuo - Kouta - Takatora. All of them have/had one "mission"; Save everyone. Roshuo and Takatora, though, were made to see that they couldn't save everyone, in the latter case being wrong. While Kouta fought to save everyone, despite what everyone was saying, hence why Sid called him a "child". All of them were also sincere, but their means were different.
Redyue - Micchy - Ryouma. All of them have/had the same characteristic; Being stealthy, tricky and backstabbing with no guilt; Redyue killed his family/backstabbed Roshuo, Ryouma backstabbed Takatora and destroying the friendship he had with him as shown in the episode with Takatora recalling his first use of the Sengoku Driver, and Micchy betraying Kouta and his friends while trying to backstab Kouta. Their attributes go on in the same direction as the previous ones (RKT); Redyue and Ryouma, as the adults, want(ed) to be the Kings, the ones on the very top, and have the apple, while the child, Micchy, cared more about the person he loved than having the power and surely didn't care about ruling. And lastly, what makes them different is how they want to use the power they want. Even if all of them have selfish desires (unlike the sincere ones that RKT had), they all want to use what they want in a different way. Redyue wants to enslave and play, while Ryouma wants to advance and rule (use the apple as a technology tool with which he could create new weapons and armors, or make his own one even better), while Micchy wants the power to eliminate Kouta and protect Mai. And this is why Sid cannot be a counterpart to Micchy. Sid is not a sneaky character, who wants power to show off and free himself from others' orders, while Micchy wouldn't care less about that.
Lastly, Demushu - Kaito - Sid. All of them share the same attribute; Desire to show their power. Ryouma may seem to care about power, but he cares about the knowledge the apple can give him, not the power itself. While Kaito and Sid want the apple because they are tired of being unimportant. They want to show that they are strong and powerful and that they deserve to be on the top of the list. Demushu and Sid, just like the other cases, have more in common (and surely more in common than Demushu with Ryouma). Sid wants to show off his power by fighting other people that are weaker than him, just like Demushu. Kaito, though, fights people on his level, or stronger ones, so that he can show his actual strength. He is also more sane and doesn't want other to see his as a terror. What non of them share is what they want. Demushu wants to destroy, Sid wants to be superior so that nobody can order him around, while Kaito wants to show that he is not a weakling and to change things into a better way, the alternative of Demushu.
I believe this is the general idea. Of course Ryouma and Kaito have some similarities, but the one doesn't give a crap about being a Duke, while the other does (pun intended). Sid may want to rule too, but mostly because he doesn't want to get ordered, not because he actually wants to. Micchy and Sid cannot be counterparts for the sole reason that the one (Micchy) is selfish, while the other is desperate, thus having totally different reasons to fight and backstab, even though Sid didn't exactly backstab, considering he was following Ryouma's orders (the irony...).