Yes grasshopper, I can assure you that this is the right path. As you can see, halving the light did nothing to stifle your Rotala growth. This should be proof positive that you do not need megawatts of light. Whenever the photonic energy input to the tank exceeds the ability of the plants to assimilate that energy, then problems arise immediately. The damage caused by the photon bombardment of light is called photoinhibition.
Photoinhibition occurs all the time, regardless of light intensity, because it is a function of the number of photon hits the chloroplast absorbs. The photosynthetic reaction centres of the chloroplasts have the capability to repair the damage, but when the light intensity is too high, then essentially, the rate of damage to the photosystems exceeds the rate of repair. This leads inevitably to a reduction in food production via an inability to use the CO2 that you are injecting because of this damage rate.
When you tank is immature it means that the plants have not yet developed a strategy for dealing with the billions of photon collisions. The photosystems therefore get damaged easily and the plant loses weight rapidly.
People are never taught to think about this stuff. Instead they are taught to think only in terms of maximal photon torpedo bombardment as if they were some kind of arms dealer in a war between The Klingons and The Romulans.
Give your plants a break by keeping the lighting low. This will reduce the photosystem damage, will allow the damaged chloroplast proteins to recycle/repair and will lower the super-oxide and free radical damage that occurs when the photosystem food production line falls off the rails. Within a few months the system will have enough muscles to cope with increased lighting.
Cheers,