Ilbranteloth
Explorer
Man, I don't have the time to read 99 pages, so I don't know if this has been said before...
But my suggestion should be "Make shields better".
If you have a shield, there could be a "Take Cover" maneuver that grants 3/4 cover. +5 AC/Dex Saves, but Disadvantage on melee attacks. Good for use while Dashing to close the distance.
If you're in a group of people with shields, maybe there's a "Form Shield Wall" that has the same effect as "Take Cover" and further imposes Disadvantage on ranged attacks against you.
Shields just provide some amount of cover in my campaign, depending on the shield type.