I think the issue people are saying is to be sure you're thinking long term.
Yes, right now, your macaw's cage will be open and it will be on the play stand all the time. So a smaller cage might be ok. BUT at some point in the next 50 yrs you will go out of town, have to work long hours, get sick, get busy... etc, etc. With the longevity of macaws, it truly isn't a matter of "if" things will come up, but "when." And when they do come up, even if it's temporary, that cage will be too small.
Better to get a large cage that will be adequate, then you're prepared for when life happens