In theory, although tomahawks, NSMs, etc. are technologically outdated, they're not more "outdated" than any tech that's used in UCAVs such as Iran's Shahed. In sufficient numbers & when used properly (e.g. with sufficient volume of fire), they are still a threat that can't be ignored. This situation is roughly analogous to Iranian Shaheds or Russian Gerans, just because you can easily shoot them down, doesn't mean you can just ignore them, especially in large volumes.
However, in the present context, one of the flaws I see with the US approach is that they trying to essentially fight an "island-hopping guerilla war" in the Pacific, where they quickly insert into some lightly defended or undefended island, fire off a few missiles, then retreat before the PLA's own "counter-battery fire" hits them. The problem here then is that the US will have a trade off between speed & volume of fire. The larger the salvo, the bigger the footprint, the slower it is in the setup-shoot-scoot process. Also, the bigger the salvo, the most space constrained they become, & the fewer choices they have for islands selection. Too large of a salvo is vulnerable & might be preempted by PLA hypersonic assets even before they fire off their missiles. Too small of a salvo & it either won't have enough volume of fire to overwhelm PLA IADS, or is too small to deal meaningful damage.