You state your running high positive (adding fuel) trims which actually means the engine is actually operating lean.
If, by your statement ” wouldn’t the plugs not firing good cause the stft and Ltft not to read correctly, due to the un burnt fuel going past the o2 sensors ”
That situation would tell the ECM that there is an excessive amount of fuel, in which to correct that would be taking fuel away (negative fuel trims)
I would think if the plug(s) are your issue to that extent.
You would be see / feeling it in the operation of the engine.
You do understand:
Higher( + 10% and above )fuel trims indicates a lean condition
Lower ( – 10% and below )fuel trims indicates a rich condition
What your stating in your last post is opposite to the actual operation of the fuel mapping system.