TL DR; The only way for a newbie to catch up on a server is to make his base un-raidable. If you want bases on the ground, make it so weapons can't do damage to structures.
Want people to stop making "un-raidable" bases? Make it so weapons don't do any damage to structures!
How is it fair that a new players on a server can't defend against steel weapons until they get to level 20?
Everyone is crying about these bases in the sky that they can't raid. Well that's because there are assholes who are griefing all these new players who have wooden doors.
You have 50 hours played on a 4 day old server, you grinded out the levels and made steel weapons, and you probably even live in an un-raidable base yourself! Now you cry that you can't reach this level 15's base so you can destroy his furnace and steal his 150 irons bars for the lulz.
Want me to put my base on the ground? Ok, make explosive pots cost way more, and make them the only method of getting into a base.
Want to raid a shitty level 10 base to grief the kid? Fine, waste a few hours worth of farming materials to get into it. Maybe then people would actually consider trying to raid the other high end clans on the server rather than griefing all the newbies.