It's a bit imprecise to say you don't go through DF if you want to avoid level sync. What's really meant is that you don't use DF's queuing ability to automatically pair you up with other people. For all instanced duties, you still use the DF window to enter them, even if you're not using it to form your group. To avoid level sync, you select the "Undersized Party" option:

http://ffxiv.consolegameswiki.com/wi...inder_Settings

Duty Finder Settings are introduced in patch 3.0. Players can access settings from the gear wheel icon on the top right corner of the Duty Finder menu.

Undersized Party allows players to participate in Duties with below minimum party member requirements. For example, running Sastasha Seagrot with 2 players. In this setting, level sync, item level sync and role requirement are ignored. Only certain duties allow undersized parties.
• Defeating enemies (non-boss) will grant no EXP or item drops. Spiritbond and Soul Resonance cannot be gained.
• Players will still receive treasure chest rewards from defeating bosses, first time completion bonuses and EXP upon completion of the duty.