Playing with LPC flap settings is against FCOM SOP guidance (at a number of companies) is likely of little benefit (as far as we pilots are concerned) because pilots do not get paid extra for doing additional calculations with different flap settings.
Your statement, allthough not wrong, goes along with the trend in aviation. Personally I find it lacking aviation common sense.
First of all, it is not merely "playing" with flap setting if a pilot choses another setting. As it seems to be against SOP, it shows that the issuers know as little about that matter than the pilots adhering to them religiously.
You rightly pointed out that the computer goes for the setting giving the most weight in relation to the lowest power setting. That's what it is programmed to do, point. The pilot however can take into consideration much more than that. For example surface condition. With an extremely rough surface he can go for a higher flap setting, as to get airborne earlier. If there are no obstacles impeding such a choice, it might be even the safer one. So why would SOP interdict that?? If windshears are predicted, icing or turbulence at low level, the pilot might opt for a lower flap setting as to get better climb performance and better power/drag ratios. If the runway is long enough and no other parameters against such a choice, why shouldn't the pilot be allowed to chose such a setting??
It all comes down to knowledge of aerodynamics and performance of your aircraft, because this raises the overall awareness of what might happen and what the values should look like. If we just punch in some numbers, and we all agree that this can go wrong, and we are only allowed to do exactly this, then we need zillions of crosschecks so it will never go wrong, instead of the good old gut feeling that this just doesn't look right.
Another point. I stated earlier that with the computers at EK, you could chose another flap setting. However you cannot chose a lesser flex/assumed temperature. This forces you to take either the lowest possible (proposed flex) or the highest possible (Max). Again, if some windshears are predicted, a low level inversion etc. etc. and you are light, the max power is not a very astute choice. Neither is the max flex . If you could reduce the flex by 5 to 10 degrees, you would be able to add a healthy and safe margin. The only way to build in a inbetween safer margin, with EKs procedure, would be to increase the weight input into the laptop. But you don't want to do that in the FMS because you'll get wrong trim settings. So there goes the crosscheck with greendot or Vref!!!! So it is very much not SOP, thus very much not recommended. With a editable flex/ass temp, this crosscheck remains fully in charge, as the procedure is consistent with laptop program, FMS and loadsheet, thus perfectly legal and safe.
I would love a more flexible programm, with a more flexible SOP as to get TO performance. It would raise not only the pilots awareness, but just as much the safety level.