There are several problems with this interpretation of the rule. But the main one is that Banking Initiative says that it "...allows the opposing force to automatically win it's initiative at 1-point Margin of Success."
The key word in that sentence is *allows*. It doesn't say "force", "must", "has to", etc.
If Banking Initiative gets to 'force' initiative in this manner, Overrun Combat is utterly and totally invalidated as a Special Command Ability.
Overrun Combat vs. Banking Initiative:
Case 1:
Overrun Combat runs into Banking Initiative and it really means "forces/railroads/ties the hands of the other player into never using their ability"
1.) Round 1: Banking Initiative forces Overrun Combat into a 1-point win -> Overrun Combat never triggers
2.) Round 2: Banking Initiative forces Overrun Combat into a 1-point win -> Overrun Combat never triggers
3.) Round 3: Banking Initiative gets an auto-win
4.) (repeat rounds 1-3, and player with Overrun Combat who designed their entire force around it is stuck with a useless ability).
Net result? - Only 1 SCA is available for play. Why bother picking any other initiative ability?
Case 2:
Now, let's look at the reverse: If it says 'allows' and Overrun Combat runs into Banking Initiative, the Overrun Combat player chooses to roll instead of taking the auto win, they can
On every round:
1.) still lose initiative, Banking Initiative takes the loss, tallies the loss for a future win ... or...
2.) win the initiative, and thus they... take an early win on their initiative.
Net result? - both SCAs are in play.
Counter argument for the 2nd interpretation:
"Overrun Combat can be used to overwhelm other SCAs." Overrun Combat's use can still be countered by several factors:
1.) Overrun Combat is best used when stacking initiative bonuses. This is done through some combination Battlefield Intelligence, Combat Intuition, Tactical Genius and Mech abilities. In the case of the mech abilities, these often vastly increase the price of units (double cost for things like PRB/RCN, C3S/MHQ1,etc.) , sacrificing firepower, defensive ability and speed for equivalent PV. So to use it, expensive units need to be purchased and heavy investment must be used just to make it work. This is it's own balance mechanism.
2.) Overrun Combat is easily countered without Banking the Initiative. Artillery, Aerospace or just Battlefield Support (strikes, artillery, bombing, strafing, mines) can all break up clumps of expensive units (see above). Because those units are inherently expensive, any AoE ability becomes increasingly more valuable.
3.) Strategic Planning all by itself allows for +2 Initiative which takes away much of the bite of Overrun Combat.
If the point of Banking Initiative is to guarantee an initiative win for both players, no matter the opposing SCA, then that happens in Case 2, while preserving other SCAs abilities to work. Case 1 just invalidates Overrun Combat by conveniently ignoring text to force players into invalidating their force.
That's why I think the use of the word 'allows' was intentional. The game wants to allow both SCA's to work.