Where did you get the information about the increased battlefield size during sieges? Regarding the general question, I voted for trusting the developers. The reason is simple: there are many new features, and it would be tedious and time-consuming to analyze them theoretically (and, most importantly, unnecessary – the game will be released faster). I am more than confident that it is possible to balance the battle on such a field, and I hope they will do so. A quick start to melee combat is neither a plus nor a minus; it is simply a new element that we should get used to and use wisely. In the end, it would be very boring to fight according to the old rules, which have been analyzed inside and out.