It's not as heavy because there's less steel in it overal, making it a great backpacking knife. The blade is plenty thick for anything you'd want a folder to doin fact, unless you're going to be felling trees or batoning logs or something, thicker blades are actually a detriment. The thinner the blade, the better the slicer, which is what makes the Opinel so great at its job.
The Endura is a good choice, but I'd actually recommend the Delica instead. I see a lot of people come looking for recommendations with the Endura on their shortlist, or (like you) a size range which the Endura fits, and so it gets recommended a lot by people who then admit that they personally carry a Delica. The longer blade really doesn't give you much, particularly since weight is a factor. Get it with ZDP-189 blade steel and you'll technically never have to buy another folder.
Backpacking methodologies usually give you a few grams/ounces to "splurge" based on personal preference, so that's where I'd (personally, being me, a knife nut) go with a multi-tool (swiss army knives included, here) and then evaluate what kind of fixed blade I'd want on that particular trip, depending on what I plan to do. Depending on the trip, that might mean a Skeletool CX, which gets you a 154CM blade and pliers/drivers for field repairs, and clips to your pack if you want.
EDIT: Sorry, I started my reply this morning and only just got back to this browser tab, so I didn't see that you'd bought the Endura. Enjoy it, it's still a great knife.