That should be a rule.
BTW, the LCS are glorified coast guard ships IMO.
Maybe, maybe not. The idea of mobility and firepower doesn't just apply to land warfare, and the LCS theoretically should have the ability of a coastal gunboat to utilize shallower waters effectively to fight, including the masking effects of terrain and bathymetry.
That means an efficient and effective propulsion system, effective fire control, shallow draft, and firepower. If you can't keep it moving, it's just a battery raft, and going to get battered.
Keep in mind that Jefferson's Navy was mostly coastal gunboats for defense, with relatively few blue water ships, but then, that was budget constrained, not blank check cost-plus territory.
The PT boats were effective for their weight class, too (and one of the most beautiful hulls ever designed, imho). And coastal gunboats and smaller vessels used for everything from SAR to defense are common worldwide.
I can't fault the concept so much as the execution, nor do I fault those who are out there trying to make it work.