A clarification, the NPL is NOT the USYSA National League. That row was not added because there are no traditional Coastal teams in that tier. And no, you cannot assume that all of those teams would have been in the National league (certainly not based on their NPL performance). The NPL is outside the USYSA umbrella. That said, those USA/MP teams would likely be in the Piedmont or Challenge, possibly National.

For those that view the forums but don't post, the USYSA umbrella looks like (from top to bottom):

National League
Regional League (here the Piedmont made up of teams from SC, GA, and NC)
Challenge (SC teams only)
PMSL (SC teams only)
Open (SC teams only)

This system is based on a promotion/relegation system as teams can earn they way up, or down, based on performance. All SCYSA member clubs can enroll teams in this league system. The admission and pro/rel criteria is publicly shared through SCYSA website.

USClubSoccer, has a similar pyramid here in the SC area (they do not have similar leagues to SCCL throughout the country though).

ECNL
NPL
SCCL Premier I
SCCL Premier II

This league structure is very different. The ECNL, NPL, and SCCL are club based with each club applying for admission. The criteria for admission varies at level and is not publicly shared. For example, every NPL age group is represented by the same 13 clubs. (My guess is GPS Carolina will take a slot from the merging of DSC and Lake Norman, but I do not know for sure if that is how their enrollment and that merger will play out).

There are several arguments of the relative strength of each format and league. Here in SC, the USClub leagues are arguably stronger. In Texas, for example, the state league is arguably stronger.

Which system is better is a whole different debate and would largely depend on what club you are at. Here in SC for example, USA/MP is in the NPL, SCFCU and CESA are in the ECNL. DSC had teams in both of those. GPS Charleston is anticipated to be in the NPL this coming season. So, for parents of kids at these clubs, there is a clear opportunity for high level play at every age group.

The downside to this structure is that the top teams at some clubs will not have an opportunity to advance. So for clubs like Cainhoy, DISA, Coast (unless their players are eligible to play at Wilmington), GPS Lexington, CFC, Bulls, Lakelands, and Augusta Arsenal, the best their players can aspire to is the SCCL Premier I. Those clubs in the NPL/ECNL will be represented there as well, but it will be there 'B' teams.

There are pros and cons to each, and how you view them will largely depend on what team and club your child plays for. The pros and cons for the clubs (and their directors are not likely to mirror the pros and cons of parents - nor should they).

Hope this helps