You are right on that dual wield is really bad implemented. But you choose a reallly bad example though.
With your wizard you only want to do it at the very beggining of the game. Early on you'll find staves with spells and better magic like abilities (specially more spell attacks rolls and DC) so you don't want to use light weapons anymore for a pathetic bonus attack that will miss most of the time and cause shit damage.
And even if a highter level you decide to get the dual wield feat, that will be for take two staves at the same time and get double bonus, not for a pathetic bonus attacks.
All that assuming your wizard isn't a race with shield proficiency. If it's, you'll want a shield firts thing
But overall yeah, dual wield should simple let you make both attacks always with your normal action, witout wasting the bonus one, and remove the bonus action offhand attack. Basically a similar tradeoff between offense and defense as with great weapons
