Honestly, there is atm, little reason to level freeze since we got the sun/moon shop. Though if they fix 9tails rewards, it'd make it easier to get adv refines. Though you can still level freeze you'll just miss out on stuff if you do.

Also, just start a fresh server and even if that server dies after a merge, * with it. Or just join an older server like S1 or S2 for example if you're worried about not being able to do GNW.

Also Merged Servers can get a merge again. But with other servers needing a merge more that haven't gotten one, then expect it to take awhile to merge a 2nd time.