Odds are we are stuck with completing challenges to gain XP to progress through the battle pass. What they should do is make it so the challenges are tied to the playlist you are playing. That way you can always have a challenge or two to go for if you don’t particularly like a challenge. So basically if you are playing FFA, they will all be FFA related… Tactical Slayer all tactical related. Of course some may argue this would progress you to fast through the battle pass. Well they could simply buff a few of the challenges. Make it take more of whatever to complete it. I think this would make quite a few players happy as they can progress in the playlist they really enjoy. Players want to be able to play what they want and progress. Infinite right now is more of play what the random challenge is telling you to play. Even with swaps you may not have a mode you like as a choice.
Then a match composer for social game types, choice between BR or AR starts… Choice between Slayer or objective games. Sure this would mean adding more game types to the playlist but it would definitely be worth the time.
You make a good point, but I have a concern:
I don’t know if they would be able to come up with enough challenges without requiring the player to play in a way that is out of their style and also potentially causes their team to lose.
And, this doesn’t just impact the individual player; this impacts everyone even when they are not focused on challenges.
Well if all four challenges pertain to that particular playlist then it would probably be pretty negligible effecting game play.
Quite honestly the way xp should work is be medal based and challenges should be bonus like in MCC. But they can improve that system by weighting the medals xp value by game types, like in objective games the objective medals would be worth slightly more than non objective and objective assist would be worth as much as the objective so hopefully players won’t be as encouraged to betray for objective if they are actually assisting. But bringing medal xp into Infinite maybe a huge undertaking.
No system will be perfect. There will always be ways to “un-sell” it or have an opening for exploiting.
“10 kills with Needler” or “50 kills with Commando” in the Ranked playlist impacts gameplay for both the individual and the team, when it causes a less enjoyable experience and/or more losses.
I think adjusting how XP works would not prevent betraying, because it’s the choice between XP or an Ultimate Reward that they really want. - they’ll choose the reward everytime. 
(I’m referring to scoring Flags as a challenge)
If you want to adjust how XP works for other reasons, though, there’s always room for optimizations. Although, from my experience with Bungie in the early 2000s, systems like this are rarely overhauled, but they could make ever-so slight changes.
Anything and everything can effect game play when it comes to gaining XP. At least if challenges where tied to the playlist you can always have challenges to go for. You won’t feel as obligated to get the ONE challenge you may have for that playlist… You would have four different challenges to go for at once.