Pumped hydro is not kinetic.

Not much storage exists because it has not been built yet. It has not been built yet because we haven't the renewable generating capacity to charge it from yet. Thus, we are spending on renewable generating capacity first, and lately factories that will build storage systems.

Battery storage is the most expensive variety. Round-trip efficiency is not very important anymore. I.e., other concerns dominate now. Anyway, gravity storage efficiency has always been fine.

Flywheels and molten salt both have pretty gnarly failure modes too. Not Chernobyl bad, but still no fun.

Underground flywheels are perfectly safe, and more easily kept evacuated. But they won't be used much at utility scale, because they are expensive per Wh stored. Maximum storage is dictated by tensile strength of the wheel material, and each wheel needs its own motor / generator.

Do you think those technologies will be scaled such that batteries are a "negligible fraction" of utility storage, or are you just giving examples of possibilities?

Numerous technologies will be scaled. Those mentioned adjacent are just very easily understood examples. Utilities will have criteria other than "easily understood", cost chief among them.

A negligible fraction of storage will be in flywheels.