That article review link you sent was interesting. "...the premise of this review is based entirely on inductive reasoning. Additionally, consideration of lower-level of evidence literature and inconclusive literature was necessary."

Here's a group that seems to focus on this issue specifically:

https://www.hypermobility.org/hormones-and-hypermobility

"...studies have not demonstrated a clear relationship between the level of relaxin and the degree of laxity. Other factors must be involved."

Seems like a lot more research is warranted. But it could be very interesting.