Note the statement "TRUE tactical"... C-17 is advertised as having "tactical airlift capabilities", but the USAF has found those are less than expected... with the aircraft being restricted from some situations Boeing had claimed it could handle.
That back-up capability is only good on paved surfaces... trying it on dirt always causes engine damage... as does most other dirt-surface operations.
The USAF loves the C-17. Not quite sure what the USAF got from the C-17 that was less than expected. The only restriction I see that Boeing designed, is the use of LAPES. But that was an USAF restriction.
I don't also understand what you mean by True Tactical capabilities vs. tactical airlift capabilities. We pretty much do everything a C-130 can do in a tactical environment. We land on dirt, we do low levels, we land on short Assault strips, we do airdrops and formation, and much more. But unlike the standard C130, we also can refuel giving us a theoretical unlimited range.
You are right about using reservers to back up on dirt fields, but that's due to FOD ingestion.