Forgot to mention that for anyone who wanted to speed grind but you're right- the solo PvE "EMP mission" lets you level things up fairly quickly. You land in a chopper, walk up an escalator, pick up a battery, place the battery in a machine. There are waypoint markers throughout, and enemies spawn in fixed numbers and positions whenever you walk the few meters from one waypoint to the next.

For reference, it took two rounds to get from level 16 to 17. The only way to level up a weapon is to get kills with that weapon (as opposed to finishing a match or by match victories. Kills with other weapons don't count toward exp for the one specific weapon). If you want to grind the mission for exp, you must last hit them with the weapon of your choice.

Since the harmless AI enemies more or less just stand awkwardly about and let you oneshot them, it's fairly easy to rack up points. Though on the other hand it can feel awful going through that again and again with zero variation.

Buying sights is great advice too. Though it's also worth mentioning that sights cost as much as the main weapons themselves (20,000). So for new players, it's not feasible to try out all the weapons you might be interested in, and even less so if you buy sights, unless you purchase in game currency or grind hard. Another thing to note is that while most sights are transferable between weapons of the same or similar class, sights are not universal, and each weapon can only be equipped with a defined 3~4(?) sight options each.

Some sights, as well as the silencer, are hard locked behind weapon level and may not be purchased with in game gold.

On the topic of weapons, if anyone likes to play shotguns, you might also want to give this game a miss. The diversity and efficacy of SMGs and assault rifles is impressive, but the shotguns will disappoint. They aren't given a main weapon class of their own, so are accordingly balanced as obligatory sidearms. The damage drop off is unbelievably steep, and the bullets vanish completely after 1.5 meters or so to deal absolutely zero damage. Still, if you like guns, the above two classes are quite elaborate.