To add to this point I’d like to go over a statement that was made by Gouken to Ken in the Nakahira SFA manga. When Ken had asked him about what a true warrior was, he questioned whether it would be sad to waste the time and energy to become so strong as to fight anybody and be able to beat them? Gouken replies that it is, and says that Ken has the right attitude going forward about it, and I feel this is another aspect as to why Ken doesn’t tap into SnH.
This care free attitude towards and impatience may be things that hinder Ken’s training in the short term of things, but his overall attitude of just fighting to fight, and then ultimately for his family, puts him on a more modernized path of the warrior. This is something that Gouken and even Goutetsu sought to strive for.
On the flip side with Ryu’s more serious and detail oriented outlook, which is awesome for training as Gouken even mentions that Ryu surpasses Ken in this regard and he’s the one who needs to keep up. The thing about it is once Gouken is out of the picture, Ryu still has a bunch of unanswered questions which get unhealthily answered by Gouki, and Ken has all the answers he wants already which is why he’s willing to innovate his techniques.
Ryu wants to fully preserve fundamental aspects of his art without it becoming something else entirely. The style is heavily focused on the Hado, and this too is Ryu’s most basic focus, which is why his Hadokens are overall better than Ken’s. Revolution in the martial arts is something Gouken managed to do as well while preserving the way art functioned. In the Ryu Final manga although Ryu gets bodied by Ken in the beginning, once Ryu starts to make his contribution to the art with the Fist of Winds he’s able to one shot Ken with it. It’s because of Ryu’s overall potential that he’s able to do this, but this will only come once Ryu has a solid answer for himself, which in the present canon between SF4 and SF5 has yet to happen.
Ken’s overall fighting ability outranks a Ryu who is not tapping into his potential (whether it manifest itself as SnH or otherwise).
Ryu’s true potential will never be drawn out with a mindset of always worrying about restraint because of SnH, but at the same time he must restrain the SnH so not to consume him, so he’s in a catch 22. That’s why Gouken tells him in SFV not to worry, not to hold back, and find out more about it.
Nothingness is an energy source, Ken has what Gouken taught to him. Because Ryu’s overall potential is greater than Ken’s, his Nothingness manifests itself more prominently than Ken’s. When Ken is fighting serious the Hado of Nothingess that Gouken has taught him is drawn out more so than if he was just fighting for fun. Even though Ken doesn’t really care about all the stuff about true warriors and Hado it goes back to what I said Ken having the right attitude. The selfless attitude of wanting to fight for his family draws out his refined Hado which is Nothingess.
Gen too has Nothingness, but this is like saying Karin has Hado energy, they can all be the same but function different depending on the user (or similarly in some cases). Karin doesn’t have access to the Hadoken even though he techniques rely on Hado, likewise some practitioners of Nothingness can defend against the Shungokusatsu while others aren’t advanced enough to do so.