Plate is vulnerable to both, zykox. If the bow draws enough weight and shoots proper war arrows with sufficiently hardened arrow tips, it will pierce through your plate at lower ranges.
But as most people used to wore something underneath, a gambeson or at some critical places another layer of mail - the piercing damage done to the person behind will be little to none compared to the force of impact and the resulting blunt trauma.
If you´re not considering it realistic that a weaker bow, like the short bow, should cause less damage than a stronger bow befriend physics.
Technically, 1h swords didn´t do a scratch on armoured foes, which is the reason they where used in quite inventive ways, grappling, hooking, bashing, thrusting and slashing the less fortunate and armoured opposition. Once you get more armour around you get more polearms on your battlefields. Clubs, maces, morningstars, huge big 2h axes, swords, polehammers and pikes become more common and counter all the canned meat. Not to mention all the other nasty little devices, like certain daggers formed to break mail and be pushed through the joints of armour.
So light infantry or weak skirmishers is and was and will most likely always be hopeless against heavily armoured troopers. Just like it should be. The only thing your basic GI Joe can do if he encounters a main battle tank is waving his assault rifle and salute one last time.
Just to use a more modern concept.
The explanation for the high strenght requirements regarding noldor stuff is pretty simple:
First of all, it´s there to avoid the PC abusing Lethaldiran as fashion slave.
Secondly, it´s there to give the player a nice and happy feeling once he´s able to equip some goodies. He´s awarded for something and will appreciate it.
Thirdly, it´s high end gear. Top of the line stuff. So it shouldn´t be available from the very beginning. This means, you have to spend some time to get it by which you´re prolly mid to late game, when personal equipment does not impact the game anymore as dramatically as it would on lower PC levels.
So it seemed quite reasonable to set it to 30. Which is something most archers will achieve non-chalantly and since a large portion of players enjoys playing archers or horsearchers it suits them well.
Me personally never used Noldor gear that much. It´s too ugly and I´m usually stuck with the heraldic mail with tabard, which is one of the best armours around. Rarely I upgrade it to Heraldic Plate or - if I get it - the Royal Plate Mail, the blue one with the yellow facings. It usually depends wether or not I can acquire a Noldor Captain Helmet.