On plate armor: This issue comes up periodically. I have posted on it several times. UO Guide's articles on Barbed Runic Kits and Valorite Runic Hammers suggest that it's possible to get armor from the hammer that surpasses what you can get from the kit. Further, if you count Samurai Plate as "plate," then you have mage armor as a free, not counted property, and can get the better mods plus meddability.
Further if you look at how armor developed there's less fictional reason than you may think for plate to be better than leather in the UO world. (That's the part I've posted about most extensively.)
There is also a post about someone creating a Sampire suit made all out of plate, here on these very forum. He had a nice journey and he was very courteous to post it for us.
And then there's the awesomeness that is Corgul's Helm. That's a great helm and its older but less useful brother, the Helm of Insight, is pretty neat too. Add a Jackal's Collar and Heart of the Lion and maybe it's worth Imbuing the other pieces as plate just for the awesomeness!
Having said that, most people clearly choose to not use plate. (I'm one of them; makes considerably more RP sense for my character to use leather.) Don't know what to tell you. Armor preferences changed IRL too.
(And further, of course there's the issue that barbed kits are way more common than are valorite hammers, which in theory are so rare that if you see more than 1 on a vendor they are likely duped, or so implied a previous community person we had. I am aware of that and am aware that in and of itself it's a good enough reason more people use barbed kits.)
I have proposed having a PvM-only damage absorption for having an entire suit of non-meddable armor in order to make all forms of non-meddable armor more desirable.
It's become typical for people to trash me when I say these things. *shrugs*
On why there aren't as many pre-made warrior suits: I don't know. I do know that I do see them on GL, just not as often as I see pre-made mage suits. But on GL pre-made warrior suits aren't entirely unheard of. I bought a couple a few months back in order to have a pre-made suit in the event that I make another new character. (Unlikely event but possible.)
-Galen's player