I see the argument that bob is making, but sadly this is countered simply by the fact that one can move their forces in the movement phase. Of course a stand and shoot army will be hard pressed in this situation, mostly because the ideal situation is to deploy and not move after that. A counter argument can be made then that allowing player to deploy where ever results in a clump of gun lines that is near impossible to tackle. Of course you can really argue anything in any situation. The counter I would say to robs deployment problem is simply that yes you must deploy in your deployment zone but after that are allowed to march in reserves from your teams side. This gives a teams reserves the chance to come in where needed. You could also say that having rob put that many titans together results in a massive firepower zone of the field, one that could very well counter many things that were thrown at it.
And for fluff reasons I'm with the whole own deployment zone idea because in an actual war a few of these armies while willing to work "together" are not thrilled about working side by side. Plus, any of the defending armies while having intel on the attack would not necessarily know how or where forces were coming with what armor or troops. I just don't see it as being fluffy that a side could really coordinate their armies within multiple deployment zones to effectively deal with what threats are dropped across from them. That is why armies would come to the fight balanced in the first place.
Color me dubious. Titans are not organized that way. Each company of infantry doesn't have an attached Titan or an attached fighter wing or an attached heavy artillery company, or an attached anti aircraft battery. These are often strategic assets organized under their own commands and spread out to cover wide fronts. You don't assign fighter wings an area of front to defend. Clumping a bunch of titans together without a screening force in front of them is absurd. We have players coming in who have been for months building forces with all infantry, others with little to no infantry. Some have many exotic big things, some have none. This last minute change is significantly impacting how forces are organized or will fight. If the game was intended to enforce balanced armies only, we should have been told a lot sooner.
I'd suggest that if a heavy force lacks screening front line units, adjacent forces with appropriate units might be allowed to spread out to cover an extended front. A primarily heavy force that allows adjacent units to cover it's front might be allowed to deploy in adjacent rear areas. This might allow players who intended to play a strategic team oriented game to deploy rationally while preventing too heavy a concentration of forces at vital areas.