I might be biased, but everything under the Division of Mathematical Sciences in the MPS directorate is important. Math is one of those weird fields that tends to touch everything else even if not directly, and it's impossible to know prima facie which areas of research will be useful downstream to the sciences and engineering.
Most of the important maths research is funded by the Department of War. NSF is a good chunk, I'd have to look it up, but I wouldn't be concerned about this at all. Math is important for the war planners, always has been always will be.
I can go for that, as long as the research proposals are actually about math research.