I guess it doesn’t happen too frequently these days someone is flying a single engine ILS in real life.
Precisely.
On B737 finals is flown F15. I start with this premise. On a normal circuit, descending or level, it is common to be F5 at least abeam the threshold. Get it under control. Thus on SE the only further flap selection is to landing flap 15 with gear down. It is not recommended = lots of thrust, to fly level in that configuration. Thus it is highly unlikely anyone would be configuring from F5 - F15 in a base turn. All approaches should have a basic plan in mind before commencing them, not just a wing & a prayer, suck it and see while it rolls along. One item in the plan is where I'd like to be F5. It is premeditated. It can be changed to suit unforeseen circumstances, but hey, that's life. That change is likely to be an extended circuit, not a shortened one; i.e. no rush. You might even stay clean until on a longer finals = no turning.
So the question is; if you believe that it is more difficult to extend flaps, slow down and keep the balance while in a turn than in straight flight, why would you predetermine to do so? If it is a normal sized circuit, and you are configuring from Up - F5 in base turn, it would suggest you have deliberately delayed the initial configuration to flap settings less than that for landing. Why would you when it is an infrequent NNC manoeuvre and one you would not do under normal circumstances?
If you don't believe this is more difficult an approach technique SE, then we shall agree to disagree. (I didn't say must not, or can not, or too difficult.) No bother. I know how I will (would have) done it on the day; but to teach that it is perfectly OK and not advise the alternative is................There are many low experienced guys out there whose handing skills are not as sharp as yours and need guidance about the KISS principles.