And if they are not hitting the supports then the supports are getting a ton of ult charge. Which means Ana can nanoboost more often, Zen can transcend more often, Lucio could Sound Barrier more often, and even Brigitte can Rally more often.
And when Brigitte Rallies Flankers lose a lot of their damage output against everything. Especially tracer.
Also the French emplacements failed because no one thought that tanks could get through the river filled black forest. This was because the concept of the tank by then was outdated in the minds of the French who still thought in WW1 terms. Instead of seeing that tanks with reasonable armor and high speed would become the thing of the future.
If the French had also setup their emplacements through the black forest then Germany would have had to either engage the mobile force that was the other “wall” to lock down the advance, or be forced to engage the emplacements directly.
Which is how a defensive comp works. The enemy is forced to engage them in order to stand a chance at winning.