And you run into the issue where some games you might want to play won't even work on MAME 2003 because it didn't become compatible until 2013. Old MAME requires less to get decent performance out of games, but like you already know, you're losing out on accuracy and bugfixes.
If you're not using some low powered retro portable or some weak ass PC hardware, there's no point in using old MAME.
You are absolutely correct, don't use the older MAME core.
