I think it's going to hurt the Victorians well before the third turn rolls around.
I'm guessing that Victorians will probably have the following modifers next turn (or something roughly like them):
Numbers: 4 points (A battalion of their troops is effectively gone.)
Troop Quality: 2 points (Unchanged.)
Air Supremacy: 1 point (Difficult to say. Since our air force is gutted, this may be higher.)
Fanaticism: 1 point (Unchanged.)
No hardened assets: -2 points (Unchanged.)
No land transportation: -2 points (Extrapolation from "Inadequate landing craft.")
Supply Attrition: -1 point (Assumed.)
Their total is 3 or 4, maybe 5. Ours is likely unchanged, and hangs at four. We'd be fighting at a tie, probably. Generously, at a point disadvantage. Either way, the loss of a point takes them from an advantage to roughly a tie. It makes it very difficult for them to score an unquestionable victory. Given their tendency to fight with human waves, lets say they force us back
again, with similar casualties. Next turn, they'd be at:
Numbers: 3 points (2 down.)
Troop Quality : 2 points (Unchanged.)
Air Supremacy: 1 point (Maybe 2 points.)
Fanaticism: 1 point (Unchanged.)
No hardened assets: -2 points (Again, unchanged.)
No land transportation: -2 points (See above.)
Supply Attrition: -2 points (Assumed.)
They'd be fighting at 1 point to our 4. Let's say they've got total air domination, which gives them 2 points instead. Then they'd only have a ten percent chance of tying. Next turn, it would literally be impossible for them to win:
Numbers: 3 points (Very generously.)
Troop Quality: 2 points (Unchanged.)
Air Supremacy: 1 point (Again, maybe higher.)
Fanaticism: 1 point (Still crazy.)
No hardened assets: -2 points (Don't think they can airdrop tanks.)
No land transportation: -2 points (Well, other than their feet.)
Supply Attrition: -4 points (Ow.)
Best case, they'd be fighting without any bonus or malus. More likely, our reinforcements and ongoing air attrition would put them solidly in the negatives. Unless we're also is really dire straits, they just lose that turn, and without resupply they'd be completely wiped out after that, since hitting a -8 modifier is effectively lethal for any army up against a credible enemy.
So it looks to me like supply maluses start biting immediately, and unless the Victorians win in two turns, they're probably doomed. Three turns from now, they probably won't be even
able to win. And after that, they probably just die. It might be worth committing more assets this turn to the eastern front, just so we can ensure the Victorian advance is stalled, because right now is the point at which they're the most threatening, and a solid defeat right now could basically eliminate them as a threat to our forces. That, in turn, would let us pivot south and prepare for their main thrust.