All spell choices of a given level are roughly equivalent; you're not gaining much power in the versatility offered versus another controller.
Sure, but context matters. Versatility
is power. In fact, it was stated by one of the designers before 4e was announced (I think in one of the podcasts), that role definition was a necessity to create balance because too much versatility equalled too much power.
Consider in your example having a player that is operating a wizard under the bog-standard rules and a player who is allowed to choose between two diametrically opposed spells like Acid Arrow (powerful single target spell) and Sleep (powerful multi target spell).
In every combat, the wizard who can choose has a
massive advantage over the wizard who can't. What about all the other characters who have been forced to choose between a power that affects multiple targets and one that affects a single target? The choice wizard is suddenly more powerful and versatile than everyone else in the party.
And that's only with one daily slot. By tenth level, a wizard will essentially be able to master any combat situation by focusing their spell choices based on the immediate need.
Plus, the fix doesn't really address the root problem, which is that the wizard isn't fulfilling its role as well as it should. I don't believe the powers of the wizard are weak, and versatility is a power boost unto itself. I do believe the current selections of powers aren't as controller oriented as they should be, however.