@GunninGopher,
You are absolutely correct, the strength of teams in a league overlaps and there isn't any bright line. Is CSL stronger than Presidio? On balance, yes. When my kid played on a CSL Bronze team (finished 4th in league) we played a few SD Tournaments and never lost to any of the Presidio AA-A teams we played (which was shocking to the Presidio parents). Does that mean there wasn't an AA-A team that could beat our CSL Bronze or a CSL Silver team? No, there were probably a few, but Presidio's next level is SDDA. Did the fact that a few years later, my kids Flight 2, SCDSL team routinely beat SDDA teams, mean that SCDSL is better, not necessarily, but on balance when you look at the strength of the programs leagues, SCDSL is going to have stronger teams.
If I'm trying to figure out how to group the various flights, levels, etc., I'm going to just look at the Cal South State/National cup level guide and call it good:
https://www.calsouth.com/en/state-tournaments/