As a matter of fact I just played 80years of a KH campaign and I fought a few battles between Athens and Euboea.

Do you have an example of someone who had a CTD with this?

BTW I've seen armies and reinforcements being positioned in the water before (RTR, I think) and except from immidiately drowning/dying they did nothing.

As for your trouble with land bridges. I thought they were easily modded out. Maybe someone can help you with that.