"Long question short....is this side trip worth it?"
Long story short, it's beautiful country and would be well worth the slight increase in distance. You'll miss magnificent panoramas of the Whitney Crest and the Great Western Divide along the JMT between Tyndall creek and the HST turnoff at Wallace Creek, but the scenery is equally magnificent in the Upper Kern Basin and devoid of the crowds on the JMT. If you decide to take the scenic byway, spend a day in the Upper Kern Basin, in the vicinity of the unnamed lake with 3 bays, and explore the basin below Thunder Mountain. It is exquisite. The trail that branches off to LSA from the JMT/Kern Canyon connector trail is signed and easy to follow to LSA. The trail from LSA down through the Upper Kern Basin is unmaintained and sketchy in places, but shouldn't present any problem as the country is wide open.
One other issue to consider: If this turns out to be a high snow pack year, crossing Tyndall creek down in the Kern Canyon could be "interesting", lots of water in a relatively narrow channel, moving very fast. If this is the case, later in the year will be better, mid August onward.