I like the balance this piece strikes between admiration and imploring for help. It is also very poetically written (which I’m sure Wilfred Owen himself would appreciate). I’m particularly drawn to your last line, “why your vision and ideas will echo across this earth for years to come and why we so hopelessly need them to.” Not only is it a beautifully written line, but it also speaks the truth in a way that is somehow simultaneously hopeful and despairing.
It terms of what could be improved, it might be worth reading your letter aloud to pick up on sentence structure. A couple of times I had to re-read a sentence to get its meaning. There is one in the first paragraph specifically that might need a second look as I get the general idea but I’m not positive what it’s saying, “my desperation in this letter finding you, is sadly unwelcome.”
Overall a nice, poetically written piece that makes some good points.