By themselves, they definitely do not have a 1-1 taste. But if you put MSG and yeast in a dish where they are well integrated (such as the casserole you mention

By themselves, they definitely do not have a 1-1 taste. But if you put MSG and yeast in a dish where they are well integrated (such as the casserole you mentioned) and evened out the salt, I'd be hard pressed to tell you which is which. That's just me though. I see what you are saying.