"I won't make any reference to conservation area/AONB then."
I wouldn't say don't make reference to it: but a conservation area/AONB "only" means that the design of the proposals needs to achieve the highest levels of sensitivity and sympathy to its surroundings, not that it shouldn't take place at all. You can still certainly try to make arguments that the impact is too great, or that the design is unsympathetic to the character of the area.
If you have an emerging Local Plan, there will be an old Local Plan that still carries some weight. How much weight the new and old plans carry, respectively, depends on how far through the process the new Plan is.
If your Local Authority can't demonstrate an adequate and well-evidenced supply of land for new housing, it's a soft target. The rule in that instance is that any policies in the old Plan that are directly related to housing are considered out-of-date, BUT there have been recent appeal decisions which have tightened up on the definition of what can be considered to be 'related to housing'... it doesn't over-rule everything.
Unfortunately, Planning is complicated, so if you're serious about making an effective objection , you should consider employing a Planning Consultant - you can be damned sure that the housebuilder you're opposing will have done so, and that's why they frequently come across as arrogant or aggressive... it's simply that they know what they're doing, whereas, for the most part, their opponents don't.