The OP is so right , far far better to play something simple beautifully than to give a "so so" performance of something harder...simplicity can demonstrate technique, interpretation and communicate so much more than just the ability to be "flash" on the keyboard, where though it is possible to loose a fluffed note amongst the myriad of others, the clarity of something simpler will silence any hall.
Personally and though I wholeheartedly agree about playing below our level for a public performance, for me that would be very very difficult

.....surely I have to have a level which I can aim beneath

...oh well, had better leave the public performances for awhile to those who are far better qualified than I.
Kindest regards....
Andrew