Those shows had large, healthy budgets. One of the goals of TNG was to create TV show with cinema quality production values. I hardly can see them enlarging sets just because they have more money.People often overlook how much of the design of past shows were simply limited by budget and resources. Paramount had limited stage space, and considering the transporter room wasn't going to be a major set we'd spend a ton of time in, they usually made them fairly small.
So this "it's too big" critique is such a silly complaint.
Now I don't think this new transporter room set is too big at all. And if a bunch of people had said that, it might warrant quotations, but "It's too big" can be a warranted complaint in other aspects of a ship. It's a starship after all, and should have a practical functionality to it, and should be built for efficiency.