Make the waaagh global giving +2 speed +30%damage to those within the range and +1speed +10%damage to those being out of range, the number can be different.
Bring back the old longer waaagh upgrade.
Add some basic healing to waaagh like 200 and nerf the warboss's doctrine from 500 to 200.
Vehicles from scraps should cost more and maybe faster generation rate of scraps to adjust the change.
All these changes or something similar will help balancing Orks vs Eldar and Orks vs SM at the same time, and also makes Orks more fun in team play.
Personally i think all faction mechanics should have less impact on game play than current ones. For example, eldar infantries can have more HP in total but less shield so they are not heavily depend on FoF. And the main reason is with weaker faction mechanics balancing will be much easier.