If they decide to make a map similar to Port Mackerel, they need to make it more difficult for a team with momentum to lock the other one in their base. More exits and pathways on the sides to get to the center would be vital to do this.
For a map like Arrowanna Mall, where players are forced to meet up in the center, design it so one really good sniper, or two snipers on one team can't completely wall the other team off from advancing should they not have a decent counter. That's one reason I've become queasy about playing on that map, a lot of matches feel too one-sided.