"I'm a soldier, not a diplomat. I can only tell you the truth."
SMG's thoughts about Burnham in Starfleet fits the idea of what Starfleet is intended to be in the 23rd Century. She'd carry that mentality forward with her in the 32nd Century.
It's really in the 24th Century that life on a Starfleet ship was shown as being more like an office job.
Janeway illustrates the differences between 23rd and 24th century starfleet in 'flashback'
It was a very different time, Mister Kim. Captain Sulu, Captain Kirk, Doctor McCoy. They all belonged to a different breed of Starfleet officers. Imagine the era they lived in: the Alpha Quadrant still largely unexplored… Humanity on the verge of war with the Klingons, Romulans hiding behind every nebula. Even the technology we take for granted was still in its early stages: no plasma weapons, no multi-phasic shields… Their ships were half as fast."
"No replicators. No holodecks. You know, ever since I took Starfleet history at the Academy, I've always wondered what it would be like to live in those days."
"Space must have seemed a whole lot bigger back then. It's not surprising they had to bend the rules a little. They were a little slower to invoke the Prime Directive, and a little quicker to pull their phasers. Of course, the whole bunch of them would be booted out of Starfleet today. But I have to admit: I would have loved to ride shotgun at least once with a group of officers like that."
The Alpha quadrant was a far rougher place in the 23rd century compared to the cultured and civilised 24th, and starfleet officers needed to be rougher as well.