IMHO, a gearing setup that based on staying out of the Big/big is a recipe for eventual disaster. Someday in a forgetful moment you’ll shift into the big/big under load. If the chain isn’t sized for that catastrophic failure can result.

Much better to size for the big/big, and stay out of the small/small. Inadvertently shifting into small/small with a chain too long for the derailleur to wrap well won’t cause the kind of damage a too short chain can.

As for the 26 we put a 26 on our Robusta, with an 11-28 on the back. It worked pretty well. However, the shifts out of the little ring were a bit slow and sloppy because the 26 ring wasn’t ramped and pinned to work with the 39 middle ring. Given that we didn’t tend to shift in and out of the small ring frequently, it was an acceptable trade off.