Several questions/issues. I'll start with the mollies. They will not live long in this soft water, so no surprise they are not doing well. I would remove them, to avoid slow deaths which I don't like to see in fish.
To the plants. First, the Banana; this is not an easy plant for many of us. Even Dr. Kasselmann writes that it only lasts about a year for her, and she is a professional botanist. Some people seem to have better luck with this plant than others. Second, the Cabomba; this is a high light plant, and with that usually comes higher nutrients including CO2. Third, swords and Vallisneria tend to do fine in moderate light. I have poor results with Vallisneria because of my very soft water. It is around 7 ppm or 0.5 dGH, and when I last had this plant it slowly melted. I am now raising the GH in two tanks to around 5 dGH (for the large swords) and think I should try the Vall again to see if it fares better. Way back (1985) I had this plant growing like a weed in a small tank with calcareous substrate (dolomite), not surprising since it does occur in hard water such as the African rift lakes. Your GH may be sufficient to keep it healthy.
To plants in general. Many aquarists try to accommodate too wide a variety of plants, and some may do well while others don't. Plants like fish have varying requirements, though with plants light is the main factor; but as I noted for the Vall above, sometimes the water parameters are important too. But light is generally the issue, followed by nutrients. We must remember that varying the light intensity also affects the nutrient balance. Low light-requiring plants, moderate light-requiring and high light-requiring plants will not generally do well together; low and moderate, dor moderate and high, can sometimes work. The "middle road" is a bit more easy with plants than fish with differing needs, but still present. Algae is always waiting to take advantage of this situation.
Over the years I have tried many plants under my light. Swords (except for the red leaf species) do very well, as do crypts generally. Java Moss, Java Fern, Anubias do well but only if in shade; but I have floating plants in all my tanks so this is covered. Pennywort is the only stem plant that thrives for me, as there is insufficient light for the others I have tried such as Cabomba, several of the Hygrophila, Ludwigia, etc. Decide what you want in terms of plant appearance, then provide the necessary light and nutrients. And with higher light than what you now have, you will probably need to consider CO2. I have never bothered with diffused CO2 and have no intention of ever messing with it, as I don't need it for what I want. Photos attached below show what can be done without it. I have managed to balance the light and other nutrients with the natural CO2.
Now to the pH. Most of us wouldn't call this "high" if the numbers you gave of 7.0 to 7.5 are correct. I assume the tap and tank are in the same range? Did you out-gas the CO2 from the tap water before testing pH?
The vermiculite might be raising the pH. I'm not sure what mineral this is exactly, but I believe I have seen references to magnesium, silicates, and others that could increase pH and/or GH. This could be very minimal, but sufficient to prevent the natural lowering of pH as I mentioned previously (breakdown of organics). Your answer on out-gassing CO2 from tap water may clue us in here.
Fish are more affected by GH than pH, provided the latter is not way off. And you have no issues with GH for the fish mentioned, except the mollies. And if the pH remains around 7, this is fine too. However, it is wise to always know what is actually occurring in the aquarium with respect to pH, to avoid sudden problems.
Byron.