I agree with this entirely.
Also, there is some tiny ambiguity in regards to the existence plate armor in LotR, when it comes to the Knights of Dol Amroth, *specifically*.
>"And last and proudest, Imrahil, Prince of Dol Amroth, kinsman of the Lord, with gilded banners bearing his token of the Ship and the Silver Swan, and a company of knights in full harness riding grey horses."
>full harness
Harness can refer either to plate armor (which is by far the more commonly-used version), or can be used as a catch-all term for "fully armored." Additionally, we do see a plate component called out specifically in the text:
>"Men of Rohan!" he cried. "Are there no leeches among you? She is hurt, to the death maybe, but I deem that she yet lives. And he held the bright-burnished vambrace that was upon his arm before her cold lips, and behold! a little mist was laid on it hardly to be seen."
>vambrace
The combination of the earlier reference to harness, *and* the explicit call-out of a vambrace, does lend some credence to the idea of the Knights of Dol Amroth - and them alone - wearing plate armor. EVERY other armor description in the books save one (the dead Southron Sam see, clad in "overlapping plates"; ie, almost certainly lamellor) is of mail.
Another counterpoint is that the House of Eorl was supposed to have some of the finest equipment in Gondor, and THEY wore mail. Also, the Byzantines were a sometime-source of inspiration for Gondor, and they did in history wear free-floating vambraces over their mail, so mail with a vambrace is not *completely* anachronistic.
So there's some ambiguity, on this one unit alone. Everyone else wore mail, straight-up. Plate armor is a TON easier to make and wear for film, though; I don't begrudge WETA switching most armor over to plate from a purely practical standpoint. This is one thing I don't think Tolkien would have minded THAT much.
>plus that choice brought us pic related; best-looking armor in the films