In my experience, one of the hardest parts of my job is talking to gamers about probability, and how it is expressed through games. Many gamers, in their heart of hearts, believe that game designers are part of a nefarious but universal conspiracy to frustrate player's otherwise perfect strategies and bring them all to an early death through sheer frustration.
Needless to say, we reject those charges. Apart from anything else, the genre cannot afford to lose a single customer!
More seriously, I would say two things. One is that things always go wrong, at every scale, in any military undertaking. The other is that if you've got 10:1 odds then even if things don't go perfectly this turn, the bad guys are probably still in deep trouble next turn.
As to the specifics in Battlefront, you will have seen in the designer notes mention of the Special Attack function. This is not limited to historical examples such as Banzai attacks, it can be used in a more general sense to indicate attacks of crucial importance where everything, including the kitchen sink, is thrown into the fight.
For example, in the Market Garden scenario, XXX Corps has an unlimited number of special attacks on Turn 1. The forces opposing them at the very start of their attack were so weak that there was no way they could hold off XXX Corps. The unlimited special attacks mean that there isn't even a mathematical possibility of this happening.
Of course, this happy state of affairs for XXX corps doesn't last, but they still get one or two special attacks each turn thereafter. This means that if you come upon a stubborn German infantry company that is sitting on the one bridge hex that is vital to the entire advance, you can use the special attack to make sure that they are ejected.
The allocation and effect of special attacks, and indeed the variability in the Combat Results Table are all under the control of the scenario designer, so even if you don't like the choices they have made, you can easily change them.