It takes a bit of study to understand how the WFCO converter/charger works and more important, WHY it works the way it does.
You can download the WFCO Theory of Operation manual here:
https://wfcoelectronics.com/wp-conte...eration-v2.pdf
And you can download the WFCO FAQ section here:
https://wfcoelectronics.com/faq/#tab-631086271d8e6
Essentially, in the FAQ section, the "experts that built the converter/charger" state that you won't be able to measure the 14.4 VDC being applied to the battery during BULK CHARGE. And, in the theory of operation document, they explain "why" it works the way it does....
I have 2 GC2 batteries and my WFCO 8955 charges them with no problems. I'd suspect that with your 4 GC2 batteries, given the extra amperage you can store and use, the "recharge time" would be two times greater than my recharge time. Otherwise, your OEM charger is adequate to keep your battery bank charged, it'll just take more time due to the amount of energy you store/use/replace in the battery bank....
As a "caution", don't rely on a bigger and faster charger without taking into consideration all of the issues you'll encounter.... As an example, higher amperage charge increases the "battery gassing potential" and that can lead to not only "dry batteries" but also to outgassing which can lead to corrosion in/around the battery compartment, as well as the increased risk of explosion from the battery gasses, if contained in a confined space.....
Adding more batteries allows for more energy stored and longer discharge times which equates to more days of boondocking before they are depleted. There isn't a "quick and easy" means to recharge them safely while preserving their reliability. Just as it takes more time to discharge them, it also takes more time to recharge them (without damage)....
I don't know of any "sure fire shortcut to recharge them in the field in a few minutes"....
I'd also suspect that your WFCO, while a "mule not a sports car" is capable of doing the job safely and effectively while protecting your investment from the potential for damage from the "rapid charging profiles" of some of the more expensive charger systems that weren't specifically designed for RV use.