So-called "civilian masters" are never a match for competent battlefield combatants.
I don't know about that, a real master would have very good combat skills, probably well beyond what your ordinary soldier or even officer would have.
It is also important to remember that civilian martial arts and military martial arts did not develop in isolation. Rather, they developed together, and often fed into each other.
A lot of the Shaoling martial arts were developed by former soldiers, officers and generals who decided to join the temple. Similarly, lords and emperors were known to hold open tournaments, where the winner were awarded posts within the military, usually as instructors to train the troops.
I also think there are many different kinds of civilian masters. You have at the one end effective bandits and outlaws, who often fight turf wars with other similar gangs/outfits.
At the other end, you have your spritualists who partice martial arts to keep fit and probably stave off bordom, and street performers who are more like entertainers than fighters.
In between, you have various martial arts schools, who often fight honour duals with each other, and the family and decendents of famous warriors and generals etc.
Of those, the gangs/bandits and some descents of military families will probably be a lot better than your average soldier or officer in combat, since that is what they trained for and have experience in.
Your spiritualists and street performers might be technically skilled, but they did not train to kill and slaughter, but rather to win honour duals at first blood or to put on a good show. So they would make poor combat troops.
I think another main reason civilian martial arts masters might not do as well as they should on the battlefield would be down to discipline and tactics.
Good soldiers fight together as a team. A pack of dogs can bring down a tiger, so unless those civilian masters can take and follow orders and work with others as team, in combat, they will just get isolated and picked off.
In pitched battles, you also have tactics and formations that are completely unknown to your average martial arts master. One guy with a sword, no matter how skilled, isn't going to be able to do much against a shield wall, pole arms and crossbows.
As such, it would be unfair to take a civilian master and just throw him into combat. You would still need to give him basic military training, but after he graduates boot camp, he should far better than your average soldier (however, sadly, being taken from civilian life and thrown directly into combat with little or no military basic training to prepare them for what they might face probably often did happen, which would explain their poor showing).
In terms of skill set and capabilities, I would suggest that your civilian martial arts master-turned-soldier would be more like today's special forces. So I would employ them as such rather than as ridiculously over-qualified line troops.
They would make excellent body guards, assassins, and line breakers etc.
The tool has to fit the purpose, I mean, if you used special forces like SEALs, SAS, Alphas and the such like regular line troops, they would do better than your average line soldier, but they would not be operating at anywhere close to their full potential.
However, I fear we may have drifted somewhat off topic now...