"top wall unit" becomes very expensive, the terraforming would cost thousands in metal just to reach the island.
I could see phantoms being useful if they made it across.
But, a djinn or charon could transport them much faster and cheaper.
With an Engineer commander, you don't even need to plate! Just use the blueprint feature.
Cutting off the western shore is a high-stakes gamble, but it could have worked out. It's a strategy.
ThePixelPirate had lobsters, Jcanibal was west of the wall and with support from a third player that island could be secured.
The big problem really is the metal and time cost of the terraform, there was no way that could have finished on time.