Here's my observation over the last 3 years of Discovery and the common threads of criticisms. It seems that the bridge crew is wanted for more development for two reasons. One, complete and total distaste for the mains on this show, from Burnham (and various rude and inappropriate sarcastic nicknames that get bandied about) to Saru for failing to live up to fan expectations in his development. Tilly sometimes escapes more often than her co-stars, but rarely. Georgiou never does save for fawning over Michelle Yeoh. So, the Bridge Crew becomes the object of desire, the "grass is always greener" type attitude common with dissatisfaction in a product.
The second one is the assumption that Star Trek is an ensemble show and it
must always be so. It fails to recall your noted extras, as well as how TOS presented itself. The Bridge crew extras on TOS were relatively consistent yet barely got lines. So, DSC is engaging in more TOS style than seems to be comfortable with those expecting TNG style.
Just my observations. No doubt I'll be told how horribly wrong I am and that since these actors are always on the set they must receive development.

If that's the case then I want Mr. Lesley to get his own spin off.