I still do leves. I find they're a decent SP boost for the amount of time you spend on them. I'm ranking up Marauder on the side so I just do leves for two camps, 1*. Generally I can get around 30k per reset just doing leves which isn't bad at all.

The system exists to allow those who either don't have groups or don't have a lot of time to spend on a given day to still progress at a decent rate.

Though for those who really want to level quickly, party grinds are really the way to go (and will be further enhanced in 1.19). I'm not a big fan of running around a small area killing the same things over and over for hours on end but hey, the system is there for those who enjoy it.