As illustrated in the map below. Notice Star Tours isn't open yet. One of those late additions you were referring to.They described Disney MGM Studios as a half day park, add on ticket to a Disney vacation, when they were designing it. The Sunset Blvd and Muppet expansions would make it a full theme park.
Early maps even describe part of the area as “Theme Park” where the 2 (non tram) rides where the first couple years. But they knew they’d need more rides if people were going to be willing to see it as a full theme park. To start, they compensated by filling the entry streets with as many characters and “real” celebrities as they could. (I got lots of autographs from real celebrities as they would schedule radio press junkets, commercial filming, and other things right out in the open that first year.)
Essentially, the park wasn’t planned well, because it put a lot of stock in the whole “actual film studio” and not enough in rides. But they figured that out before it even opened, with expansions already planned. They just ran out of time to build them.
In other words, you’re both right lol. It was a half day park, but they called it a theme park.