It is a near certainty that in any game like World of Warcraft where there is an incentive to progress and a punishment to failure that a system using talents and stat points will produce optimal builds. We have seen in the past many one trick pony builds exposed and curtailed quickly because players were not doing what was expected. Ghostcrawler has recently confirmed this approach once again by ensuring that retribution paladins (and protection though that is a smaller issue) will not and cannot make effective usage of spell power plate for fear that they would become over powered as healers. This of course seems a rather odd decision given that the overhaul of talents allows paladins to have only a few and inefficient heals directly within the base paladin architecture.
This approach to KISS is in many ways sensible, if there is only one build then that is the build that will be used and the game can be easily balanced around it the other approach however of allowing multiple builds including what would formerly have something like 31/0/40 holy (sheatheadin iirc) exist within the meta. Indeed this is explicitly what other games do. Taking magic the gathering as an example, the core set of each expansion brings 350 ish new cards into play with linked mechanics, an the. Two smaller expansions related to this with their own internally consistent mechanics. Each time a new set is introduced we see old decks adapt to the new using the new cards as well as entirely new decks formed from the new set with cards that might have been considered worthless in the previous set alone.
In WoW we have a very stagnant game controlled by evolution of power rather than mechanics. Imagine instead of the gear evolution what altered was our capabilities. So on Naxx we might have our basic abilities, the 31 point talent trees we know and love with say 35 talent points. When you clear naxx not only does your gear upgrade scaling your power but you gain access to new abilities as well. Each new tier brings out say an 11-16 point talent tree and some new talent points. Each tree is focused toward the fights of the next tier allowing blizzard to create fights that a normal build could not handle, but by the last tier allowing extensive customisation.
Of course this isn't new, subclassing has been known nearly forever in role playing, however making it dynamic bases on the new training and technologies we have unlocked would be interesting. Each new tier would be a new mini game with a new meta and each new expansion a consolidation to the 'best' talent tree.
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