So, some people don't want to spam the same buttons, but some people also don't want to lose some skills because of button bloat...you'll eventually reach one point where you won't be able to please all of them, and choices will have to be made. And one of the decision doesn't change the actual flow of combat, so I feel this would be less troublesome to getting used to.
But, that's consolidated skills. There's not much difference between Raiden Thrust replacing True Thrust when "raiden thrust ready" or Vorpal Thrust replacing True Thrust during combo. Same for Nastrond and Geirskogul, VerHoly/VerFlare or Scorch replacing earlier spell "combos".
Setting the same combo multiple times wouldn't be that a problem, but even then, if you consolidate combo as an option, you'd still have to take into account that people won't use the same number of shortcuts when adding new skills.
Again, it has nothing to do with how the system could be added to every combo without massive development cost since the template already exists.
Being a theme park is not an issue. Right now, I'm pretty sure you could clear any content except Savage and EX primal without even applying Darkside once. The added complexity would be for more advanced players and when tackling endgame content. And frankly, consolidating combos would be more new-player friendly since it would guide you through your basic combo. And, it would be much more friendly to controller players, since it would allow more skills to be placed on the right side of the crosshotbar, which is much more comfortable to use.