I wouldn't necessarily say that, since i've seen shops use them on larger tanks, they just tend to turn up the bubble count and have a current pointed just above the Co2 diffuser to push it Co2 bubbles around the whole tank
I'd suggest an inline diffuser from greenleaf aquarium. Or just DIY a reactor. I really like the micro bubbles with the inline though. I read somewhere that a mist of co2 bubbles spreads through a tank better that co2 that has completely dissolved in water.
i have he atomic inline and overall it is a good diffuser. I just don't like how you have to have another one on hand and do clean it every three months.
You just need some good water movement to get the co2 moved around the whole tank. When I use them disc type diffusers I always make sure my water flow is directed to push the co2 around the tank.