Honestly, "gym rat"-ing did more to get my kids' skills than anything and it's hard to do that when they're young.
As far as "gym-ratting" goes, whether it helps gain kids skills really depends on the type of "gym-ratting" they're doing.
There is Good Gym Rat who is at open gym every day actually working for the entire 2 hours. Asking coaches who are there for tips, getting tips from more experienced friends, and are generally "in the zone" for most of the time working on skills. I am not generally a fan of kids being in the gym when it's not open gym or practice/private/class but these kids don't bother me.
Then there is the Annoying Gym Rat who is at open gym everyday for 2 hours, is all about "getting her full" but in reality, for a 2 hour open gym, she spends:
20 min - taking a selfie in her new sports bra and bow she just got.
30 min - talking to that boy she likes.
10 min - stretching while talking.
10 min - in the restroom
20 min - getting water after having not actually tumbled yet.
10 min- shooting youtube vids of her and her friends being silly on the tumble track.
5 min - actually throwing tumbling.
10 min - watching people tumble and being like "omg I want to get that sooooo bad."
5 min - saying how bad she wants abs.
These are the kids whom I have to personally walk up to and tell them that they need to either be working on skills or leaving because they are being distracting and taking up space from the kids who are actually in the gym, you know, WORKING.