You do need the IQ4.
AFAIK Optimas are AGM, not "gel"
You seem to be suffering from undercharging by not getting the batts high enough in SOC with the gen running to then leave the rest to the solar at this time of year. The IQ4 will let you get higher in SOC for the same generator running time as without it.
That causes "progressive capacity loss" where each incomplete "cycle" leads ever downward in capacity. You need a truly full charge followed by an "overcharge" (called a "conditioning charge" with AGMs) to restore your batts to good health.
Your solar is likely ok, but you need more (" quality" gen time this time of year--IQ4- before letting the solar do the rest before it gets dark.
