Honestly, this could be to the game's benefit. Reducing the size and scope of the world seems like it's letting them creating a more fully fleshed-out and detailed environment for the game to take place in. I find that to be preferable to the vast expanses of nothingness that made up Scarlet & Violet's map.
If Lumiose City ends up having a full game's worth of depth and interesting things to do in it, that's a concession I'm willing to except, especially since the generation 10 title rumored for next year will likely iterate on the concept of open worlds in the series.