They had to make Saru a bad captain so Burnham could take the chair. Though to be fair, I don't think it's unreasonable for a brand new captain to make some mistakes and I enjoyed the mentor / mentee relationship between Saru and Vance. That being said, Saru did seem a lot more competent at the beginning of the season than he did at the end. Of course now that Burnham is captain we all know she will do everything perfect the first time and will always be right about everything in the end.
I thought Tilly as XO was a ridiculous choice but she really didn't do that poorly given the situation. What they never explained was how Osyrra was able to beam through Discovery's shields so quickly. That really shouldn't have happened, particularly with the ship upgrade. It's like, Vance is a real idiot for sending his only spore drive around the galaxy by itself with seemingly no protection against being boarded?
I thought Tilly as XO was a ridiculous choice but she really didn't do that poorly given the situation. What they never explained was how Osyrra was able to beam through Discovery's shields so quickly. That really shouldn't have happened, particularly with the ship upgrade. It's like, Vance is a real idiot for sending his only spore drive around the galaxy by itself with seemingly no protection against being boarded?