That is not it at all.
The difference is that when they got ambushed, the non "combat arms" unit basically fell apart. They were not trained and experienced in the use of their weapons, their weapons were often sadly lacking in basic maintenance, and they did not know how to behave as a "combat unit".
Other than Infantry and a few other MOS, no other MOS seriously trains in actual combat proficiencies. And yes, I have seen this first hand. I spent 10 years as a grunt, where we did that kind of thing every day. As a squad leader more than once I would take my squad out in garrison (especially if we got new members), and train and drill them in basic skills. Crossing danger zones, hand and arm signals (both common and squad-platoon specific), reaction to ambush, all of that stuff. We drilled and operated in many squad and team formations.
Our SOP in performing a Squad Wedge formation was to put Team 2 in a wedge, team 1 in an echelon left, and team 3 in an echelon right (I am aware most non-grunts will be lost at this - in essence it makes a huge wedge formation). The first time I tried that in the Army (non-combat MOS), the instructor asked me what in the hell I was doing. I explained what I was doing, and was told to do it the way they told us to do (each team in a team wedge formation - essentially 3 diamonds).
However, after the training was done he pulled me to the side and said that yes, that was how grunts would do it. But we were not being trained as grunts, so we did it different.
There is a reason that for most of the last 12 years, I was either in Force Protection, or in OPFOR. They recognized my background and mindset was much more oriented to those tasks than that of the rest of the "PATRIOT" people, or even today in the medical unit I serve in. I know how to use my weapons, not just the basics. I even remember instructing my unit armorers what a "scraper" was for an M249.
They all had seen these in the armory, but none of them actually knew what one was, or how it was used. I had to teach the Battery and Battalion armorers how to use a basic weapon cleaning tool that every E-2 learns in their MOS school. I knew how to keep my weapon clean at all times, and to do something as simple as a range card, or how to use a T&E. Most of those not in actual combat arms do not have a clue how to use them.
That is why the 507th Maintenance Company got slaughtered. Not just land nav, they had no idea what to do when they came into contact with the enemy. They did not know how to react, they did not know how to lay down an effective base of fire, they did not even know how to properly use their crew served weapons to protect themselves.
Talk to most who are like me, who go from grunts to another MOS and we are generally shocked. Things we take absolutely for granted they are absolutely clueless about. Even if a grunt unit had gotten lost and ambushed, they would not have had the same outcome as the 507th had. 11 KIA, 30+ WIA, 6 POW.
The company was hit with a hasty ambush, got divided into 3 segments, and the tail element was overwhelmed. A more "combat trained" unit would have realized that even after it started to take fire, they should move on and find another way to reconnect with the rest of the unit. In essence "punch through", get clear, and reassess the situation. Not return into an urban area where it had come under fire and try to retrace their steps.
As a grunt, I have been part of a unit that got lost many times. The doctrine is to move into a clear area without known enemies, recon the area (either map or visually), make contact with upper echelon, and plan a new route. Not go right back where you took fire already just because it was "on the route map" and try to link up again. You are bouncing back to the land nav, and completely missing all the other ways that they did the wrong thing.