Some thoughts on : No USW
IOTL the losses to subs were already increasing from August 1916 onwards to somewhat around 350.000 tons/month, wirth a slight tendency to further increase (January 1917 368.521 tons) (
source).
Well before USW, though its was still/already a theme discussed by the germans.
AFAIK this was to the most extent due to the german sub-production finally kicking in sufficiently for a 'war-time' industry.
Now ... ITTL without USW and US-entry, the british ability to fight of the german subs even on cruiser rules would be reduced at least (
less oils for ships, less escorts, if convoy-systems would still be adopted as there are less ships also).
That in turn would increase the number of available subs for the germans.
In this situation it would be IMO well within range of the germans to increase cruiser-rule sinking to something around 400 to 420 k tons/month.
Still far from the IOTL by the germans envisaged/hoped for 600.000 tons, you might say.
True, but ...
The Brits are now without the US-entry quite short on cash to buy :
food for the british people
oil for the british warships
ships for shipping whatever can be bougth abroad
ships for protecting convoys (destroyers)
and therefore the "ratio" of british ships to be sunk for fighting down Britain also decreases, which with the increasing numbers of german subs available ... vicious circle with a not well ending on the british side IMO.