I’ve never heard of corals or nems getting stunted. It’s really just a matter of having enough space to spread and food/light to grow.
Bta being recommended for a 100 is due to the fact that they grow and split fast, and will sting/kill nearby corals. Frankly that’s a rather excessive recommendation - you can keep one in as small as a 10 gallon. I wouldn’t keep one with corals in less than a 30-40 though.