Yeah Nintendo said it was designed that way, but I've definitely noticed an increase in give as I've played. Though it may also be because I fidget with them the more they give. The right one makes a freaky noise and I absent mindedly rock it back and forth whole playing. Was thinking about tightening the screws, glad to hear it works. I was super impressed at how rock solid the connection was when I first opened it.
Mine was snug fit first day. After a week, it wobbles so much and along with springy sound from thumbstick, I bought a new joy con. New one is now tight. I'm sure it will get more loose overtime. Looking at teardown on the bottom part of the plastic rail just hold by plastic so it might wear with use. Time will tell if it gets more loose.
My new right one also creak at the bottom but only if I try to bend it does not happen during play. I now only use the old one for split use only and my new joy con will never leave the console.