My idea of fluctuating CO2 would be a system that is set daily by trying to achieve the same bubble rate with no solenoid to keep a set rate of flow daily or a low tech tank with weekly water changes where you upset the balance by giving the plants a small amount of CO2 one day a week (or 2) when the tank would be better with changes every other month, thus causing you own algae problems. As for yeast or DIY, I would consider that not to be constant but the changes may be slow enough not to have a negative effect on the system, but I've never tried yeast.
I can say water changes do lesson the amount of CO2 in my tank so I try to do them early before it comes on but it's so brief I don't think it matters much and just one of my dysfunctions.
I also agree with the natural build of light with a mid day burst, in most areas the sun is strongest for a bout 3 hours a day, this also lets CO2 build. I'm also a fan of lights out for 30 minutes after mid day just as you would have a tropical thunderstorm after the heat of the day, this has worked very well for me.