I've noticed that FASM doesn't set this field in PE header total correctly - say when there is no reloc directory entry the field still doesn't have IMAGE_FILE_RELOCS_STRIPPED flag specified, also IMAGE_FILE_DEBUG_STRIPPED flag too should be specified as we dont have any debug sections. Am i correct about all of this?

IMAGE_FILE_RELOCS_STRIPPED was set by older versions when the image was relocatable but relocations were not put into it (and thus stripped). For the currect case, when the image is not relocatable by default, I thought the "stripped" flag would mean the wrong thing (as there is nothing to strip in such case).
Some of those flags are anyway loosely interpreted by many tools, so I too interpreted them in my own way - too carry some fasm's specific info.

IMAGE_FILE_RELOCS_STRIPPED was set by fasm 1.66 depends on relocs present.