In any situation that isn't solo or lowman with friends, closing a skillchain is near impossible. Someone will always weaponskill after you do, even if you have a party macro stating you're about to skillchain.

Sometimes if you're lucky enough their weapon skill will chain off your first one and given the correct element can sometimes provide interesting results if you then weapon skill off the resulting chain, but it's still annoying.

Theres a reason people say "skillchains are for solo content" People want things to die in seconds, and unfortunately it takes longer than that to set up a skillchain + magic burst.