When you mount FAT32 in Linux, your mount options and /etc/fstab file determine who owns the files. You're right that chown/chmod/chgrp are meaningless for files on a FAT32 filesystem.

If the files on your card are RO, it likely means you need to umount and fsck the memory card. Once any filesystem errors are cleared up, you can mount it RW again.

Anecdotally I have much less trouble with ext2 microsd cards than I do with FAT32. Only occasionally, after a major system crash, do I have to fsck ext2-formatted cards... but with FAT32, it seems like they'll go RO for the tiniest reasons. Similarly, as long as ext2 FS'es are made with "-I 128", I find it easier to work with ext2 on Windows than I do FAT32 on Linux.