I was at level 20 well before finishing the campaign. If you do the adventures, hit up a couple public events along the way, you get there pretty fast. If you're just focused on doing the campaign though, then 18 sounds about right.
And yes, as you might have noticed, gear all has random perks again (this was missing originally but D1 had it), so it makes it all that much more important to infuse gear that you like and has decent perks that match your game style.
Honestly, with all the daily and weekly things to do, it can be overwhelming. Though I guess before there wasn't enough as you could finish in a few hours, now it takes either a solid day or a couple hours over the course of the week.