Actually, having worked concession stands in my youth(95-98), this isnt totally accurate. Although I can see why you would think this. Both football and basketball had similar "rushes" to soccer. In fact I would stand around doing nothing for most of the game except at the beginning then halftime. While during the game you would get like 5 people coming up sporadically. During halftime it will get incredibly busy but the staff would try to be prepared for this by having premade food and having dedicated pourers. I dont think I ever really got a "training" session but they did put me with a more experienced person to show me the ropes the first day. And it wasnt rocket science after the first day I knew how to do everything.
In football, baseball, basketball, and even hockey there are so many breaks in action that concessions see a more steady flow of people. In soccer, there are no breaks except at halftime.
Granted both GS and Continental Arena were around for 20+ years by the time I got there and some people there had been with the company since the stadium opened. They did a far better job than RBA does. And training SOME of the staff DOES pay off. If youre able to increase the intake by even 10% that more than pays for their training day and hiring a trainer(who is probably someone on the Del North Staff already)