Damn, I didn't know there's only 4 Lego cars. That's disappointing. I've only unlocked two. There was plenty of Hot Wheels cars in FH3.
Then again, the map isn't smaller than Fortune Island and there's the same amount of story chapters. Plenty of other challenges, collectibles and events too. So, while I'm not sure it's the biggest expansion it certainly ain't the smallest.
It's 18 with game pass sub so like Barozi pointed out, good value for LEGO stuff.