Maybe not in the very truest and most technical sense, but consider the case of compression clothing.
Compression clothing is believed to improve performance and recovery times when exercising and many people swear by it. However according to this article, there is little to no evidence to suggest this is the case, or why it would be the case.
And here's the important bit; despite there being no evidence and no reason why it would improve your performance, those people who believe in it feel they perform better. In other words it's a placebo effect.
Now I doubt modern compression clothing is possible in an historic setting and I'm not sure old fashioned corsetry could do the job, but really it doesn't need to. You don't need your armour to actually do anything (though something noticeably different about it would probably help) all you need to do is tell your warriors their armour has been enchanted by the most powerful mages in the land, or blessed by their gods, and they will feel stronger.
It may not be the kind of effects games prescribe to magic items, but it could still give that performance boost.