possibly a dumb question but i'll throw it out there anyhow: so if i'm running an older iMac on El Capitan am I 'forced' to update to newest OS to 'be safer'? I keep older OS because my computer runs fairly smoothly with my hardware peripherals and various software.
Will adding antivirus programs really buffer my defense with these specific attacks?
Pretty much yes, you need to update, unless Apple issues security updates for older OS versions, like Microsoft does.
No, antivirus programs won’t help because the nature of possible attacks is such that attacking code doesn’t do anything illegal from their point of view.