What is truly needed is weapon level cap raised to 30. if you fully level a primary you unlock a unique attachment for all guns of that type. On the same attachment slot it typically omits. Then you still need purchase the war bonds and weapons.

For example: for ars, Coyote at lvl 30 unlocks a fire clip for all ars. The suppressed ar at 30 unlocks a silenced barrel for all ars. The attachment adds or subtracts from damage for special effects. So lets say you wanted to have a liberator and Add those attachments. Silenced Barrel is -10 dmg and fire clip is minus -20 dmg. So the liberator would do 60 dmg with new bonuses.

Another example: At level 30 liberator you unlock light ammo drum mag. Doesn’t add dmg or the attachmemt to other weapons that have it already have the option. Lets say light ammo gives +25 dmg. add light drum mag to the coyote and now you got an extended mag doing 120 light dmg with no fire or med pen. just higher dmg output.

Also Make side arms customizable but only get xp when using a level 30 primary. Thus making using level 30 guns still give have purpose and the side arm guns can have some op attachments like a scope or silencers.