Maybe you should invest in better infiltrators. 
When one of my realm-mates get stabbed by an enemy infiltrator, it's usually a serious wound or worse. I think I've ever only seen one instant-heal since the new wound system was implemented. Normally the victim is out of action for about one to three days, even for young nobles who are supposed to heal quickly. If it was anything, it was a major buff for infiltrators.
Sounds like you guys want another class. One that has less risk, less training time, and less damage output to compensate.
Basically you want "infiltrators for dummies". 
Personally, honestly, yes. Grandfather the current infils into staying as such, but don't make the class available anymore for switches. Create a new saboteur class with a bunch of low-risk options that require less training, and fine-tune into it being more of a "demolition expert" than a ninja.
