Phileas, as a reminder the discussion is about the viability of DSA (because SZD was deemed unviable, so people don't think we have hijacked a thread!).
LPL's runway opened in 1966, so 32 years before 1998 = 3 decades.
LBA started commercial services in 1935, and was operating holiday charters in the 70s = 2 to 6 decades.
Either way the facilities in operation by 1998 had been in place longer than DSA has been open.
Any deficiencies at either airport in the past, in a comparison to DSA now, are offset by your own point about lack of catchment area at DSA. So I guess that makes them all equal for comparison purposes.
Anyway, I think it best to return the discussion to SZD.