What would you consider the worst thing to happen to dust why?

For me, it's cloaking devices. Back in beta, battles were alot more honest. NO ONE could charge straight at an enemy squad or clear out a whole whole single handedly, yet today because cloaking devices (and other mechanics related to scouts) I see it often.

Situation awareness used to be a thing, until CCP literally took it out of the game. There's no skill in being invisible. Cloaking devices never added anything of value to the game. It broke game balance so badly that it took months of buffs to other suit classes just to compete. If CCP would ever remove anything from Dust 514, I would want the cloaks to go away like black ops tanks did, and never come back.

Aim assist is the worst thing to happen to this game.

I've never really had any problems with dust. The cloaks were cool and added some variety; BUT what they did wrong. Was they didn't balance the game when the cloaks were introduced.
The exact same issue with tanks back in beta, 90% of the player base was brand spanking new so all we had were MLT and STD AV to take on PRO tanks. So really the forum whingers won and got tanks hella nerfed at the same time as us beta guys started catching up to get PRO AV, whilst the tankers only had STD variants, so there you have your imbalance.

The same issue is in cloaks vs scans. Only ONE suit could scan the cloaked+damped scouts at the time. That scout had a HORRIBLE buggy hitbox that has now been graduated to the min assault suit. But the scans were nerfed into the ground when the cloak was introduced. Therefore every suit bar ONE always got snuck up on while trying to protect or attack a point regardless of how many scanners you used to try and create 'situational awareness'. Which is where everyone's frustration over cloaked scouts has stemmed from. NOW cloaks are nerfed into the ground and guess what, scans are OP again because a cloak is too slow to activate to utilise in an attacking momentum and doesn't provide any benefit to any suit BUT ONE.

SO TL:DR

The worst thing for me in dust was CCP never finding the balanced medium for their changes. Making one thing way too OP for 3-4months while we bare with the burden hoping the next update will nerf it

it still doesnt make sense that there one suit that can move around completely uncontested. and its only counter is one other suit using a mostly useless piece of equipment.

CCP add suedo scan fall off but nerfs scan range into the ground so that the net gain is less than what had started with.

"oh we have to nerf scan range so nova knifers can still nife people in the back." they gave concession to the most niche and non viable thing related to combat. i rank it up there with hull tanking in eve online in terms of usefulness. yet the whole scan mechanic suffers for it.

and balance? god. theres no weapon/ suit balance between races. which suit is best with Scr? which suit is best with CR? how about AR? any suit works. how about RR? any suit works. hell the gal assault suit uses the RR better than the cal assault, because it can deal more damage, tank more damage, get remote reps, rep through damage, and deal damage at the same range as the cal assault. so thanks CCP, the cal assault is out classed by other racial suits using the cal assaults own weapon. and we've been over it for month with Rattati but he does nothing.

PS. a kick reduction bonus to the RR isnt as good as an optimal range bonus