I think its ridiculous to even consider Dog Logan as Sabretooth, as much so as claiming that Rose somehow was reincarnated as Jean Grey.
That's a gross exaggeration. There's
plenty of good reasons for people to assume Dog is Sabertooth.
1.) Sabertooth and Logan were intended to be related, Chris Claremont has said so. Though another writer changed that later, they never cut out the possibility of them having some other kind of relation, such as being a brother or half brother.
2.) Sabertooth has had a feud with Wolverine that has dated back almost exactly to around the time Origin ended. The episode with Silver Fox was in the early 1900s. Origin ended in the early 1900s. Origin also gives Sabertooth (if he is indeed Dog) a perfect reason for hating Logan.
*Logan got the nice rich dad while Dog/Sabes got the poor abusive dad.
*Logan spent more time with Rose, who Dog/Sabes had a thing for.
*Logan killed his father and got to run off with the girl Dog/Sabes liked
*Logan stole his name
3.) Logan and Sabertooth have extremely similar mutations, so it doesn't seem to odd to assume that they may be related in some way.
4.) Sabertooth has memories of an abusive parent. Dog had an abusive parent. While Sabertooth's memories are of a different father abusing him, it's been stated that he doesn't even know if those memories are real (because of Weapon X tampering with his mind). Weapon X could have simply took his memories of being abused and changed it a bit so he wouldn't know his full past.
5.)Then there's Dog's appearance. He looks like Sabertooth, and when he fought Logan he acted just like Sabertooth. The only, and I mean
only thing that set him apart from Sabertooth was that it appeared his healing ability wasn't powerful enough to heal away scars. And that can be easily explained away, as I've said before. Besides that, it appeared Dog had all the attributes Sabertooth did.
He was big, strong, and he tracked Logan to the middle of nowhere with nothing to go on, something Sabertooth has been able to do year after year on Logan's birthday.
To say that assuming Dog could be Sabertooth is crazy is simply faulty logic. Personally, I think it's a perfect origin for Sabertooth to be Dog. Not only does it tie him closer to Logan, it adds a bit of tragedy into their story. They're two brothers, but all they've been trying to do for the past hundred years is rip each other's throats out.