I think one of the unfortunate drawbacks to 4E's design is that it assumed you could keep all players constantly engaged during combat instead of them zoning out when it isn't their turn. I looked at the 4E Cleric's powers last night and there are a lot of little short term effects with specific requirements, such as:
Given the nature of the AEDU system these features will only come up once per fight each unless they are at-wills, meaning they are less likely to be memorized through repetition. That can be a lot for a player to keep track of themselves, much less reminding their fellow players of. I can see how these kinds of effects promote both teamwork and engagement and like these in a vacuum, but I think the system could have benefited from fewer, more consistent ones.
I also think that having more potential options for simple to use and remember classes and power would have benefited 4E. In my experience running and playing 5E I've had some players who are very interested in tactics and having all their character's abilities memorized and others who routinely forget what modifiers to add, what feats they've taken, what racial abilities they have, etc. People have different levels of willingness and capability to devote to knowing game mechanics by heart. 5E and editions other than 4E accommodate for this by having a range of complexity from relatively simple to complex, but 4E seems to be designed exclusively for intermediate to advanced players.
Oh, you're completely right that a wider spectrum is valuable. I do not question this.
My assertion is twofold.
First, 5e was designed with the theory that
most things need to be tailor-made for the math-averse folks TwoSix described. That's a problem, because it can very easily turn off the folks who
want more. (I'm sure someone will come along and give 3PP as a solution, and I've already said elsewhere why I find that not actually a solution.)
Second, that 5e has continued past editions' flawed, bad, damaging, rigid link between spells = complexity = flexibility (and thus power), while martial = simplicity = inflexibility (and thus weakness). There is no such thing as a simple spellcaster (I'm sure someone will come along and give Warlock as a counter-example, and
no, the Warlock ABSOLUTELY IS NOT simple.)
If we're going to take the "a spectrum is needed" response seriously, there needs to be a spectrum across
thematics, not just in the generic. There needs to be at least one spellcaster that is comparably simple to the Fighter, even if it's still a
little more complex (e.g. Battle Master level). There needs to be at least one martial that is at least
comparable to the Warlock or Sorcerer. And we really,
really need to fix the whole "simple things are usually weak unless heavily optimized, complex things are usually very strong unless played incredibly casually" problem. 5e has taken baby steps on that front. There's a lot more that can be done.