It’s one of those “in a perfect world” scenarios.......that yes, front and rear fuel flow on a square bore carb with equal sized venturi on all 4 barrels would be equal.

But many times it isn’t all that practical...... especially on something that gets driven on the street.

Often times after you get the primary side really dialed in for low speed and part throttle operation..... having the same jet/air bleed combo on the secondaries leaves the wot a/f ratio not where it should be, and/or not making the best power.
So, the secondary side ends up getting the final adjustments for wot operation....... and you’ll often end up with different fuel flow on the two ends.

If all the circuits are operating correctly...... you should be able to end up with a situation where there isn’t a big discrepancy between front and rear.

Keep in mind, not all carbs are “square”.
There are many carbs out there with different sized venturi between the primary and secondary........ and those would rarely see equal fuel flow from both ends(why would they?).