The only way to solve the portal issue is to solve the weapon xp grind first.
Why not make it 500 kills per gun to hit lvl 50 and unlock all weapon attachments/camo's? This would bring back players who left because weapon leveling takes too long.
You could then bring back "full xp & stats" to portal servers regardless of the "bot backfill" or having "no bots" option, and make them 1 player to start which would also bring back players who left because portal was ruined.
Another option to make portal interesting would be having "Battlefield Templates" where you could make portal servers from previous BF titles. For example: It would be cool to use a BF4 template where all the game settings/movement/vehicles/TTK would all be as if I was playing BF4.
Maybe dice should incentivize and reward players with better QoL updates to keep them playing, instead of frustrating them till they stop investing their time, energy, and money into a game that seems to get worse every season?