Maybe your problem is attitude related. Turning your nose up at newer players and reluctantly allowing them in when you can’t find someone “better” isn’t going to leave them feeling welcome. Consider them an investment.
New players face a relatively easy but intimidating early-game meta and can crank out trophies, and an established guild’s mastery bonuses will prove an enormous benefit. Even a moderately active guild will output keys that will grow a low level player’s collection and gems that will buy them those tantalizing armors, whereas a high level player is just farming duplicates for the ascension grind with keys and gems.
Before you know it, that level 60 recruit is a level 200 sentinel grinding out 200 trophies a week and donating 100k, and the best part? He’s loyal to the people who helped him get to where he is, and he’s happy to bring up the next lowbie looking for a home.
tl;dr: Most of my best guild members were low level recruits.