That's only because Smugglers' skills are front-loaded and Knights (Guards especially) are back loaded.
Heck, at launch, Guardians really didn't get anything besides their level 20 spec skill until 35ish. They didn't even get their basic tanking skills (taunt, guard) until much later than Vans/Shadows. Fortunately, Bio realized it was a huge oversight and quickly remedied the problem within the first couple of weeks.
But yeah, Smugs get a lot of goodies early. This is especially true for Slingers who reach close to 90% efficacy by level 30 (or even 25). For most it's not a big deal, but it has been a point of order in the PvP community.
Even dps scoundrels have to wait until 36 & 40 to get their two best skills.