Something you should have checked is what items is he using. In my games, I noticed he wasn't very smart in that regard.
Also, I just want to say that this map is fucked up, and you had a huge advantage. Kraxis had no room to grow. If he went south (which I believe he did) he had nowhere to place his first city for roughly 30 turns, with a lot of fighting at the start. Not only that, his only alternative was to head back and go north, which is usually no better than the first direction.
If I was in his shoes, I would most likely lose as well for these reasons. Something he might have been able to do to solve this issue was to create a scout and go north. This might not work, though, due to monsters, and being unable to dodge them in such a narrow path.
I would like to add that, if I would ever start in a position such as Kraxis, I will ctrl+n for a place not stuck in a corridor.
Continuing with the map:
From what we can see, roughly 50% of the map is impassable, and 70% of the remaining land is covered with trees/swamps/rivers. This leaves us with quite a bit of land we can move "normally" on. I would really like it if it would be possible to reduce the amount of impassable land, and maybe somewhat the amount/effect of the "slowing" areas, allowing greater mobility around the map.
For quick reference, the CIV games we all know and love, and MOM, had roughly 20-80% of the land covered by large water bodies (which are passable by boats), and about 50% of the land with forests (which were cut down in civ) and hills, letting troops move around much more efficiently. The land is usually either a continent, large island, or small island (depending on choice), so nearly 100% of the near area for expansion is reachable, and only 50% of it slows you down. In a similar 1v1 game in CIV, the amount of impassable land will be insignificant.
Another solution is to allow the sovereign to level the area for his needs, and not in a crazy manacost.