Well, short version - people abuse it farm EXP. Instead to play the game, two player just run to a relay and the attacking one spams use so that he gets EXP for taking the Relay and the defending one for returning it INSTEAD TO PLAY THE DAMN GAME.
I now got kicked twice for playing the mode as intended instead to farm so there is CLEARLY something wrong with that.

One fix would be that neither, returning or taking would gain EXP anymore - only a successfull capture ( which has then 100 more EXP of course)

Yes. How many times have you killed the guy stealing your relay only for someone else to run over and return it! Maybe a +50 bonus for killing the stealer and the rest for the person who get's a point.

Still people would abuse it somehow. Co-operating to deliver relays back and forth. Some people are just low. I remember when I used to play BF2142 you would get losers who would go to the enemy base and spend entire rounds just throwing EMP grenades at commander assets. This bagged you .5 of a point. I mean seriously why would you spend money on a great game just to sit there for hours and hours throwing grenades at static objects.

You can see servers around with 'don't join or ban!!!!!!' as the title - these are the domain of lame booster dikes.

Well, if they would cooperate to let it look like they would play the game it would at least SOMEWHAT of an improvement - that means that if there are people actually playing the game wouldn't really bother and it would also take A LOT more time to farm EXP so that in the end, it might be better just to play right away.

I see no issue with someone wanted to quickly level up to pass all the grinding required to get the weapons. Personally I would have rather had an option to unlock everything at once, there is no skill to grinding and anyone who wants to skip it should be allowed to.

At least shooting the fuel tanks of enemy jeeps parked in their base rewarded you with constant explosions in the original/Wars.

Well, if I'm on a server and they're boosting, I just run around the map and wait for more players to join. As soon as more players are joining, the game is automatically running according to the rules, because the majority of players wants to play CTR, not BUTR (Boost Using The Relay)...