Model type

During "Model setup", there is a choice of Helicopter or Helicopter The choice of "Airplane" has never been an option. Frankly speaking, I don't think it is needed since everything is done wit the mixers.

Is it a good idea to just delete this option?

With the arrows you can also select "Airplane" (but no options behind this).
If you click on "Helicopter" you get to the swash mix settings.
I confess the plane flyers are less supported by deviation than the heli flyers are. Most naming is for helis. But as you said, with the mixers you can do whatever you want, even support planes with many flaps (or how these things are called...).
I have encouraged more than once that some plane flyers tell us what they need but most efforts came to nothing.
Conclusion: the option is necessary and will stay.

While writing FDR has overtaken...