I"m pretty much at a loss on the front chainring issue unless I can see it in action.

If it's able to overshoot the big ring at all, the parameter is set too wide.

A wildy out of parameter rear could do what you say: chain toss when you're on both outer cog and outer chain ring.
In my opinion, That's possibly indicative of both chain stays bent to the R. They may be parallell, but over to the R.
That could produce both the steering and the shifting problem. Just a guess without seeing it. clues would be at seat lug area, where the seat stays meet the seat tube, and at the rear of the bottom bracket shell, where the chain stays meet the shell.

Good mental work, but I've already exhausted my supply of mental.