Yes, Aliens are indeed bigger than their hosts, but we aren't talking something that grows several times bigger than the host. Look at that thing. Assuming the picture is in perspective, so we aren't seeing everything in the same place, that mountain, and the mysterious rock, are pretty distant. And that means that the supposed Jockey Alien is
f**king huge. Godzilla ain't holding a candle to that thing. It's enormous, hell, it covers a side of a Mountain.
The Jockey isn't that bigger than humans.
Maybe twice or thrice the size, that's it. We'd have a way smaller Alien from that.