Speaking as a long-time WoW player, myself, it's worth noting that default class complexity (baseline) and mutually exclusive complexity (e.g. talents) are very separate things, and that pre-combat choice can often come at cost of in-combat choice. Talents, for instance, can be made such as to newly allow or disallow baseline toolkit options. Unless the removal of any given part of the toolkit allows new things to be done with the remainder (think Decimation or Demon Blades) that are more attactive than the greater spread of original options (because of a greater number of new derivative options), then that ends up making customization one step forward and two steps back. There's a lot to get wrong, and often talent systems have taken the blame where that would more accurately fall on a gutting of baseline toolkits or a rebalancing of the individual abilities to make their use more obvious, but thereby narrowing the range of their use (e.g. AoEs that will never see ST use unless talented into, rather than crafting situations by which the key is still useful).
Not remotely. Here:
Basically,
Fundamentally,Out-of-combat choices (i.e. in customization) are siphoned from would-be in-combat choices.
Effectively,Character combat-related customization is limitation. It is, definitionally, denying assets already made unless you have selected all the relevant choices.
Stl;sdr:A particular class will still see only a given amount of complexity as per developer goals and time-budget. You can have that complexity available at all times, or split up such that only certain glimpses each are given through customization. Adding customization does not increase total complexity, but it may reduce effective complexity (sometimes for the better, sometimes not).
Customization =/=> Complexity.
Instead, sometimes there's just enough, or even too much otherwise, complexity to pare it back via customization.