Why wasn't Sabretooth the original Weapon X subject? Wasn't he trustable, or were his healing powers inferior?
I don't recall that this has ever been specifically addressed, but I believe that this passage from Wikipedia is the most spot on.
The character Wolverine is depicted as his long-time enemy, although conflicting accounts have been given as to the origin of their feud. It is also known that he and Sabretooth were victims of the Cold War supersoldier program Weapon X, and that Sabretooth saw Wolverine as competition and tried to make his life miserable. While Wolverine is depicted as suppressing his more savage qualities, Sabretooth does the opposite and embraces them.
Remember that the Weapon Plus program is a military program, with the goal of creating super soldiers. Even without being enhanced, Sabertooth was problematic, being a serial killer with no remorse. Even if his healing factor was advanced enough to handle the adamantium bonding process, he would be a poor choice to provide with indestructible weapons if they have issues controlling him.
Comic Wolverine has received (and lost, and regained and ad nauseam) boosts to his healing factor and adamantium lacing to his skeletal structure though not as complete as Wolverine's (Typically the joints and ligaments are not covered). Various retcons over decades of writing, Sabertooth is generally considered to always be an equal match to Logan, neither having the upper hand aside from moral differences.
The same can be said for 19999 MCU Sabertooth. Origins (which mind you, may or may not be canon anymore due to the events of Days of Future Past) shows Sabertooth and Logan equally matched.
There are four logical, practical reasons Stryker would want Wolverine for the project over Sabertooth.
- Adamantium is rare and in limited supply. Wolverine has an overall lower stature and body mass. In the movie, then entire reserve of adamantium for the procedure is used (a continuity error with X1-X3). Smaller size, less adamantium needed, more adamantium to use for Weapon XI.
- The bonding process is considered highly risky. There is a significant chance of death. Why risk losing a useful asset like Sabertooth when you can use some smuck that deserted you instead?
- He believed, rightly, that he could trick Wolverine into the experiment.
- Risk Management. Sabertooth is a basically an amoral mercenary willing to kidnap and murder other mutants, and Striker is not a complete idiot. He knows that Sabertooth will betray him if given a reason to, so no need to make him essentially invincible. Again, see 3. (Bonus, Creed already showed signs of instability at the start of the movie, not following orders)
Note, the movie does have Sabertooth angry with Stryker, demanding the Adamantium because they had a deal. Stryker says that the tests came back, and that Sabertooth would never survive the procedure. As to why or if its the truth is not known. Kayla (Silver-Fox) also says that Stryker is using them, as he also hasn't held up his end of the deal to release her sister, right after Stryker tells Victor he wouldn't survive.
Comic Sabertooth WAS an original Weapon X subject, along with Wolverine, Silver-Fox, Maverick, John Wraith and a few others.
Through a patchwork of retcons in the last 3 decades, it has been established that Wolverine was the first to receive the Adamantium lacing process. At the same time, the entire subject team underwent brainwashing, memory implantation, assassination conditioning. After the Adamantium bonding, Wolverine went beserker and destroyed the Weapon X facility and almost all the staff. The other test subjects escaped, including Sabertooth.
It has not been established if Wolverine was supposed to be the sole or just the first of the Adamantium experiment subjects, as those in charge had died before it could happen.
The Weapon X project has since branched off, and new Weapon Plus projects have also been created. In the mean time, Sabertooth has continued to be involved with other Weapon X projects, and has received and lost adamantium lacing as plots required.
Remember, that Wolverine and Sabertooth's past have always revolved in fake memories, government conspiracies, brainwashing, memory erasures, and a blood feud. Most of the backstory revolving Weapon X is told through the character's view point, and is not the most reliable.