is the XTC the daddy of the Sherpa?
Umm, maybe not so directly as the eXp and the earlier, derailleur-geared (original) Nomad. Both those were aimed more at heavy touring, insofar as I can see, and more likely begat the Sherpa.
According to my 2001 Edition of Open Road's Encycleopedia
, the xTc (Ecstacy?) was described as "...a light all-round tourer, suitable for long day-rides, moderate off-road use, and lightweight cycle-camping". In contrast, the eXp was described as "...a true workhorse, perfectly balanced with a full load of luggage".
At the time, the line also included the Nemesis, "...an ultra-lightweight sports tourer for those who want a quick-handling, multi-function machine. With a short wheelbase lugless sealed-tube frame, it responds with lightning-quick, road-racer handling -- yet it's tough enough to perform manoeuvres you'd never think of attempting on a racer. Couriers, apparently, love it!".
Other models at that time included the Nomad, Audax, Brevet, Club Tour, six tandems, and two triplets.