Yeah its a tough one. Most established shells are requiring more stricter requirements but for good reason. A lot of time is invested in creating and maintaining a linkshell with events, socializing and getting together to do stuff and achieve common goals. With the way SE has set up the current linkshell management system (basically not much there) it is difficult for linkshells to ensure they get players that can commit the time needed to integrate into the shell. It is difficult enough when you start in an established shell to get to know people, learn peoples quirks etc but when we add level restrictions etc it gets even tougher. The reasoning why we do this is because we have had a lot of people join us in the past that say Hi for a couple of days then decide they don't like FFXIV and just leave, meaning that we are left with another player on our shell list taking up a space that a more active member could use. So we have recently introduced a minimum level of 30 as we think that means that a player has spent sufficient time playing their class to know they enjoy it and want to play some more. Remember you are half way through your r50 journey when you are at R40! so even r30 is quite low still. I think that also in our shell we spend a lot of time chatting and working together crafting etc and we also don't want people just joining to leech off us (e.g. get us to craft items or go on event runs just to get a piece of gear and then move on to another shell once they have got what they want). In terms of the hours per week, 5-10 hours doesn't mean you cant play FFXIV and enjoy it, far from it, however to really be part of a linkshell you have to be active and 5 hours per week for instance doesn't really give you a chance of getting to know members and taking part in shared activities. We have found in our experience that players who play for 20+ hours tend to integrate much quicker and better and stay in our shell so we are putting in that restriction so that people don't waste their time.
At the end of the day for us it comes down to playing together, mutual respect and a shared sense of fun and challenge. As a new player I can see why this might be seen as a bit of a barrier but you have to understand the reasons why we put restrictions in. :)
There is always the option of creating your own shell and getting players that you party with to join in. In a way thats how our shell was formed over 8 months ago!
Good luck in your hunting!