I think this is because Bally invested in, and managed to hire, programmers that knew what they were doing. AFAIK williams' first programmer (system 3) was an electronic organ programmer, and quit when he got a job back in that industry. Until Williams hired Eugene Jarvis and Larry Demar, they didn't have a clear vision/person able to drive the development to what it became. Eugene Jarvis because he made stuff 'cool', and Larry Demar because he made stuff structured.

Bally's software sophistication was dominant until Stern mpu200's pigs interpreter, which blows away Bally's straight 6800 assembly in terms of what you can do with the game without writing a bunch of stuff to compensate. The Centaur/Flash Gordon era bally tried to graft things in to do lamp effects, etc. but it wasn't as easy to program as pigs.

As soon as Williams went system 7 with Larry Demar's version of a virtual machine, forget about the sophistication of the other systems. Far superior in every way (software wise). Much more flexible and designed with extensibility in mind. Of course, required way more resources than the earlier stuff.... the framework Larry set up though carries through to the end of williams pinball wpc95, there are elements of system 7 in every system since then (although they abandoned the interpreter at the end of system 11). The multitasking switching is the same system though. (extended in wpc). (all this not counting the 2 pinball 2000 released games, no idea what they did in terms of any of this...)

Bally's always bricked even when new.
Williams actually can as well if someone bends the copper spring back too much.

Can you bend the shelf like I did with the bally mystic center bank? I had a devil of a time with Lightning's center bank when I had it as well and I tried some pretty radical things with that one and Free fall's. Have not had the occasion yet to do it on any other sterns, they all seem to work fine at this point, but I only use vintage drops. If I need new ones I'd go swinks but I have a large stock of vintage drops to choose from. Maybe tweaking the angle just SLIGHTLY will help. I used to shoot to the 'side' of the lightning drops to try and get them down, but clearly that's not intended. I know I show bally drop in the pic, but bending the equivalent part on the stern bank is worth trying.

My theory with the ledge bending is that any downward pull in the target will negate the bounce back onto the shelf.
The ones in my mystic still can brick but there's a different drop in the center that one is the worst but clearly a different plastic.

Can you pull out the two screws farthest from targets on the shelf and tilt it a little bit just to test the theory.... Then you can come up with another way to permanently mount.