That's how I bleed them, but sometimes it takes more. 8-10 activations would be normal to get the air out. Sometimes more. I vacuum bleed from the calipers/slaves, then do several 30-0 activations on gravel. Grass would be OK, I think. Anything that allows uneven friction.

Your codes may be in history. If you lose wheel or speed (tranny output) sensor values, the ABS won't work, at all, and the ABS lamp should be on. There are so many reasons for weak brakes, the ABS is pretty low on the list. Other than having air, it has no effect on overall braking until there is a traction issue and ABS is activated. Maybe have a look at the mechanical side of it. Good discs/drums and pads/shoes are essential. Blowing a line changes all of it, and puts you back to square one. Drying up the master cylinder is another issue. If it was used that way for any amount of time, I'd likely just replace it. They don't like running dry, and plunger or bore erosion happens very quickly, especially if it's aluminum.