I looked again and I guess I missed where the poster said they were going to limit their training solely to the couch (still can't find it!).
Now if you are referring to static training in-water then I would say that it would be difficult to find a better way to gain comfort in the water than through the most fundamental way. Now through your static training I can only hope that you are training correctly in which you have an additional focus on improving the elasticity of your ribcage, conditioning your diaphragm, breathing properly, learning to induce relaxation and lower anxiety by gaining feedback from your static holds, and how to effectively take a "screening inventory" during the hold, among others. If this is the case, I would be willing to bet that your scuba will benefit from your static training. Even if you spend all your time on the sofa, there are many who train "dry" and receive some benefit from this while freediving so why wouldn't this extend to scuba as well?
But don't take my word for it! Go train and then go scuba and draw your own conclusions!