Portal farming is the symptom, not the cause

Whoever decided to lock attachments, gadgets and class passives behind assignments really didn't think things through.

Because it actively punishes new players since they have to grind these assignments vs people who have them already.

That slows progression down so much that it becomes a severe balance issue since so much of a weapon's output is dictated by what attachments it has. Grip and Suppressor specifically come to mind here, they change how a gun operates entirely.

It also screws with their data. How in the hell is DICE supposed to know if something is over or underperforming when 85% of the game's population will never get to test that weapon/gadget/class trait out.

This is why people were spamming XP farms. Because DICE soft locked people out of meaningful levels of progression which are needed to even have a chance vs this sniper/smg meta.

Just separate bots from no bots servers. Bots have everything unlocked so no need for farming while no bot servers get xp and progression, more competitive play style

Many of the challenges are too difficult or downright impossible, but people farm regardless of whether progression is fast or slow. As long as farming is faster than just legitimately playing the game, people will have an incentive to do it. Because why wouldn't you seek the path of least resistance? 

Portal is supposed to be more than just bot farms. It's that simple.

Solo/coop mode with everything unlocked is better, they could even make things you do in the portal editor available offline for testing or for messing around in.

True, so speed up weapon progression and cut bot exp totally would be the right choice, but DICE decided to play deaf

They didn't decide to play deaf. They specifically acknowledged the issues with challenges, but they also mentioned that it would take them some more time to work on it. 

All DICE employees should play in multiplayer and get 150 kills using a sniper from 200 meters away before they can get paid. Let's see if they will design the same assignment in the future.