It's not about being unable to produce sufficient CO2 with fermenters, it's about the massive pain in the ass dealing with several 2 liter bottles is, and the inconsistent flow rate that will be much less beneficial than the precise level you can produce from a pressurized system. A 250W metal halide is also extremely high light for a freshwater tank, especially if it is shallow.
Compact fluorescent is still widely used, although it is less efficient than T5HO in terms of total light output and reflector design.