Dam I had an inkling that they would be bad, it would put World War One on par or worse than any other conflict the US has ever had in your worse case.
The US got off fantastically lucky for casualties OTL, if they had to deal with the same grinding attrition of the other Entente armies it would be a bloody affair indeed.
I think if the US enters 2 years early instead of merely making up for the Russians withdrawing, they'd speed up the war by a lot more than 1 year. They might be able to wrap it up by Christmas 1916, before Russians had any thoughts of revolution.
Not so much. As others, and myself, have pointed out, despite the size it had a small army and virtually no one with combat experience or a mass pool of reserves and artillery. It was not yet the 'Arsenal of Democracy' of 1941-45. However, doughboys stop a bullet as well as anyone else.
If TR makes some movement towards preparedness in 1914 maybe they can move faster than OTL and really get into the fight in 1916. However, I don't think that they'd have the same impact until 1917, which still probably neuters the German plans for an extreme victory offensive and the Germans fall back to the old German border to defend the homeland.