Now I hadn't run into this particular battle before though the result, a soviet victory against forces of about equal numbers suggests that they could have well pulled it off given the superior numbers they'd dedicated to the invasion of Hokkaido. The fact that you cast in doubt the outcome that is so clearly laid out is rather curious.
Did you not read further? The Japanese capitulated because of the
general surrender. The Soviets barely got a beachhead before Japan surrendered.
Never head of the Atlantic wall then? The Normandy landings faced twice as many divisions as there were in the entire whole of Hokkaido, while the particular placement of the Normandy landings was always in doubt ( though the Altantic wall didn't exactly have gaps in spite of this ) there were always a concentration of forces ready for an Allied invasion in Northern France, unlike the Japanese and Hokkaido.
All favorable landing beaches in Hokkaido were fortified and manned. They were also manned by actual Japanese troops, not the second-line reservists (to put it charitably) the Germans put up in Normandy. And yes, the Atlantic wall was a thing, but you can build all the concrete bunkers you want but if you put them in the wrong places and man them with what can be charitably called second-rate conscripts they do you no good.
At Sword beach the Allies had 683 casualties.
At Gold beach the Allies had about 1,000 casualties.
At Juno beach the Allies had about 900 casualties.
At Utah beach the Allies had about 1,000 casualties.
At Omaha beach (where they faced an actual first-line combat formation) the Allies had about 3,000 casualties.
At Shumshu the Soviets lost about 1,600 against token resistance on an island not nearly as heavily defended as Hokkaido. Not only that but they lost 5 landing ships in the process.
If, as you've stated yourself, lend-lease provided a huge amount of supplies to the whole soviet union through the ports in the pacific I imagine that they'd do fine just with those.
What are you talking about? How do the Soviets
get supplies to Hokkaido? They can't just beach merchant ships, they have to have a port to supply a sufficient force. Where is that port? How will they seize that port? How will they seize that port
intact? Hokkaido is a really big island and they will need sustained offensive operations. Where do the supplies come from for those operations?