Yes, early UU's are often shirked for their real power, which is both in the early advantage they give you as well as the fact that they upgrade (often) into superior midrange units. The Jag is no exception: You think a Jaguar is scary, imagine the logistical boost alone that a bunch of Swords or Longswords with Woodsman gives, not to mention their ability to self-heal off of kills. Plant their upgrade version in jungle as well, and they're fighting at combat strength of one upgrade higher (at least til Muskets).
It is mirrored in other early unique units as well.
Pictish Warriors are scary enough as is, but they become really terrifying when you realize they become Pikemen with the strength of Longswords when not on defense, and then Lancers with almost Cavalry strength. (Not to mention the no move cost pillaging retained... at lancers this is just... yikes)
Similarly, Immortals are great, but midgame, having Pikes/Lancers with permanent Fountain of Youth healing on them is just daunting.
Likewise, I always shrugged at Slingers until I realized that they turn into Comps and Crossbows who have withdraw before melee, at which point I realized they were a lot harder to get rid of.
Sometimes the best thing to remember about the early UU's is that they don't always "obsolete", they often turn into something even more terrifying than their original iteration.