I'm sure others here will disagree, but high loads through a conventional socket and plug will cause problems eventually, much better to wire it as a fixed appliance and take the plug and socket out of the equation. NOTE: the 'quality' brands such as MK are better in this regard.
I'd only disagree with your description of MK as "quality".
but thats probably another thread for me vs. world and his dog.
But other than that you're right, whatever the rating may say, oxydisation, dirt, wear, poor manufacture or whatsoever, plug-and-sockets aren't the ideal solution for long term high loads.