Looks like the binary size optimization flags are not ideal when compiling with MSVC.
On other compilers (gcc/clang) the current size optimization flags lead in most cases to smaller libraries. On MSVC this seems to be not the case, the libs often get larger when optimizing for SIZE.

For example jvm.dll (build with VS2022) with current -Os size optimization
20M images/jdk/bin/server/jvm.dll

with -O1 set for size optimization
13M images/jdk/bin/server/jvm.dll

See the doc from MSVC about "optimize for size"
https://learn.microsoft.com/en-us/cpp/build/reference/o1-o2-minimize-size-maximize-speed?view=msvc-170
"The /O1 option sets the individual optimization options that create the smallest code in the majority of cases."
The Os option is only a part of the size minimization flag set :
/O1 (Minimize Size) equivalent to /Og /Os /Oy /Ob2 /GF /Gy