having an XP system in place will not stop people from ruining games by farming challenges. I played enough games that have both to know they don't...
those challenges need to go, all of them.
if it's not "win a slayer match", "have a positive K/D in Slayer" or similarly straight forward challenges then nothing will change.
especially egregious are the vehicle specific ones as they completely ruin big team, you can tell many players try to prolong the game so that tanks spawn because they need to destroy one as a challenge... and how do they do that? by sabotaging.
I have seen multiple way people did that, either they ignore the objective like the enemy flag or they outright help the enemy team if you're about to win.
(I have seen people juggle those energy thingies to the enemy base because our team was only 4 away from winning)
this will never stop, there will always be those to hardcore farm them.
how hard can it be to only have challenges that promote good gameplay? too hard for 343i to figure out I bet