I think what makes the resemblance seem so strong at first glance is the ceramic bezel. Zenith has gotten around this problem partly by using low-inertia silicon for the escape wheel, but a lot of the mitigation comes from customization of the driving and coupling wheels, each of which has a unique profile for the gear teeth. The amount of energy available is even less than at the fourth wheel, and adding the load of driving the chronograph is potentially even more problematic. The problem is even worse if you try to drive the chronograph off the escape wheel. Balance amplitude can drop significantly when a chronograph is switched on, and if the watch isn't in optimum condition, accuracy can suffer if you leave the chronograph on for long enough.

Driving a chronograph from the fourth wheel is already kind of pushing it it's the last conventional wheel in the going train, and stealing energy from the gears at that point means less energy is available to reach the balance.

The reason you don't usually see chronographs driven by the escape wheel is that, generally, it's a terrible idea to try.

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