Mate, I am a battlefield vet from way back in the day!, and I can assure you that this change has been absolutely appalling. Simply put, DICE promised full xp for using official rules and modes in Portal and thats what they should do! all the bot lobbys should rightfully be shut down if they have utilised higher than normal health for the players vs bots, or even like in some modes where the bots dont have a gun at all. That is not in the spirit of what most real gamers are trying to do.
if you have BACKFILL on with no password protection, and no modification to anything such as health, movement speeds, loadouts (aside from open or closed weapons) then there should be NO XP penalty.
What they should do is completely remove bots from portal and normal multiplayer (they only added bots due to the 128 player games in 2042) and give everyone a solo/coop mode with either its own watered down progression or with everything already unlocked.
I honestly think they thought doing a campaign this time would keep pve players happy.
