The basic difference between Altay and AK is the operating environment. AK is made to order to operate in the Plains of Punjab and Deserts of Sindh. Altay is designed to operate in Turkish operating environment which is much cooler and the ground/surface is harder. Furthermore, the operating ranges also differ. This coupled with heat levels, presence or absence of water bodies; infrastructure and dust levels are some of the things that dictate the specs of both the armored fighting vehicles.
AK has been operating in Pakistani environment for almost a decade now. Lessons have been learned, operating doctrine has been established or modified, keeping in view the capabilities of the AK/T-80UD/T-85 in strike elements. The cost of induction of a new tank will also include the cost of a thorough evaluation of our operating doctrine which would require time, money and re-training.
AK already has a number of westerns (or western influenced) designed and supplied components including FCS, Optics, Gearbox, Power Pack, etc. Therefore, not much can be gained from Altay here. As far as armor is concerned, it seems that technology sharing has been done by us rather than the other way. In fact, if there are systems and subsystems that are way up their in state-of-the-art, we will not get it due to the "Chinese" factor.
On top of that Pakistani Army personnel have been involved in exhaustive evaluation of various western tanks for KSA and are fully versed with the capabilities of their western counterparts and Directorate of Armored Corps is in possession of these detailed studies. I know atleast one person who was involved in the French AMX 56 and Leopard II evaluation in KSA.
Altay, might be an excellent weapons platform for Turkish Armed Forces, would have serious handicaps while operating in Pakistani conditions to name a few; Weight (Eastern part of our defenses are based upon natural water bodies assault bridges would be required to launch counter attacks that would require assault bridges of higher ratings higher induction cost!) Same is the case with the railway rolling stock! Furthermore, due to extremely dusty environment, all year round, a number of changes would be needed in the air intake filters for the engines (Remember M1 Abrams). Heat is also another element where Altay might have some problems, especially in the deserts of Sindh and Southern Punjab all of these modifications generally add to weight.
IMHO a better bet for Pakistani Armored Corps would be to stick with an AFV which was designed from inceptions as a Pakistani specific AFV well suited for our operating environment and level of education and training. Yes, there are areas that need improvement including faster loading time of the Auto Loader (Not that it is slow but can use faster cycle times), Enhancement in Snap Shoot capability, Anti-Helo capability, Anti missile warning and defense capability (As rightly pointed out by one of the contributors on this thread we will seldom see a Tank on Tank battle anymore but more of a Helo or Anti Tank vs Tank engagements) and reactive armor as a standard.
My 2C worth.