Darn
Where's "Pat" when we need him.

Now to answer the OP

Lets look at what the majority of fliers were using 5 years ago.
Glow engines - with one control - the throttle
Simple radio installs (mostly PCM) with basic battery systems (Usually Ni xx Technology)

Wow - we must have been killing a lot of people at the field in those days - very little 2.4, no optokills, no chokes etc. No wonder our insurances are so high

Why do we want to use a remote kill now?
The main reason people use them is because they can (as they are available) and because it gives them a warm fuzzy feeling.

A choke servo is a good thing to use for a kill in an emergency - as long as you have power and radio link to operate it (or failsafe set to operate it in the case of a loss of radio link). however Many use manual chokes these days.

An optical kill is similar comments to the above except that the loss of power will also cause it to operate - as long as it is in good condition and has been set up right (I have seen them fail on a number of ocassions - including some that allowed the ignition to stay active).

The best insurance for not needing either to shut the engine down?

A good quality installation and good condition equipment.
Use good quality equipment
Set the throttle so it wil in fact shut the engine down completely - test it regularly as they can wear and not to that job.
Use good condition battery packs.
Use good condition electrical connectors
Use a proven method of enigne mounting and throtle linkage.

When was the last time you actually saw a plane lose electrical power in the air when it wasn't caused by "owner error" ?

Yes - some of my planes do in fact have optokills (I use the smarfly units exclusively nowadays) ALL of my planes will shut down on the throttle and ALL of my planes have the failsafe set to shut the engine down on throttle (as wel as on optokill and / or choke if fitted).

Have I ever used one in flight? - Yep - the reason? I was getting glitching and killed the engine for safety reasons as there was quite a crowd at the airfield - the reason for the glitching? - User error (spark plug cap not properly installed).

So to answer the OP's last line

No - you are not missing anything at all.