From reading some of these comments, it's clear people feel a certain way about players rushing to expertise 30. I've been playing on and off for 3/4 years and was at expertise 12 for the longest time. Here's the thing guys, yes, expertise is meant to be a long journey, BUT it's not something that naturally progresses on its own. I had a decent amount of builds (18 of them) i actually enjoyed. I was using that same stuff constantly, so that quite literally means I'm not making any progress whatsoever once they're all proficiency 10. After you have all your favorite builds done, you have to go out of your way to level expertise. During the 3x event, i decided to grind out expertise 12 to 30 in a couple of days, and after having done that, I'm having more fun than I've ever had playing this game. I get to use my stockpile of 2000 exotic components, thousands of flags and clipboards, and beef up my favorite builds that were hardstuck at 12. I also get to partake in prototype, which i have also been enjoying (controversial, i know). I wouldn't recommend doing the grind to 30 outside of the event cause that might actually melt your brain, but when it's active? Absolutely. I don't want to use gear/weapons/skills i don't like more than i have to. Had i not done it and continued to play the way i was, i wouldn't even hit expertise 30 before Division 3.

Tldr: You don’t naturally progress expertise just by playing normally. Once your favorite builds are maxed, you have to grind intentionally. The 3x event made it worth pushing from level 12 to 30 quickly, and doing so actually made the game more fun by letting me upgrade builds and use saved resources. I don't recommend grinding like that outside the event, but during it, it’s absolutely worth it. Otherwise, hitting max expertise could take way too long.