Well, I think that 802.11 is not that bad. Conceptually, the way it schedules packet transmissions over time turns out to be quite efficient (at least in WLANs scenarios), even though this efficiency is somewhat reduced with newer and faster PHY layers (packets transmission being faster, the time spent in backoff to avoid collisions increases the overhead).

From an engineering point of view, my personal opinion is that the fact that 802.11 operates in a completely decentralized way is probably more desirable than having a more complicated solution that would require AP-to-AP communication but would most likely provide only marginal gains (several researchers have shown the close-to-optimal nature of purely decentralized CSMA-style scheduling). In case of spectrum assignment, it can benefit from AP-to-AP communication, especially if you want or need to enforce particular optimization criteria, such as maximizing throughput or fairness (I've personally experimented with that kind of algorithms as well). But often the overall gain does not justify the extra complexity.