There is a minimum amount of light that you need before even the best CO2 system will help. Once you get above that, then CO2 is the best investment for an enjoyable planted aquarium. Years ago, when the only lights easily available were T12 fluorescent lights, the main struggle was getting enough of those bulbs over the tank to get above that minimum light requirement. That led planted tank enthusiasts to be obsessed with getting more light. Then, when PC lights became easily available, people started using more light than they really needed, and CO2 became essential to avoid growing mostly algae. Now that we can use T5HO lighting, far too many of us are still obsessed with getting more and more light, and we can end up with so much light that keeping enough CO2 in the water without killing all of the fish becomes a full time job - not a hobby, but a job.
A hobby is supposed to be fun. And, it is when you use only enough light, so that the you can grow all of the plants you want to grow, and have a pressurized CO2 system to keep them supplied with adequate carbon for optimum growth.