"HERE'S TO SICKLY SEASONS AND BLOODY WARS." - Famous British toast.
And as an example of promotion jumps.
Pershing - Captain to Brigadier.
Custer - 2nd Lieut. to Brigadier(Brevet)
In the case of Custer, the Union Army at the start of the war numbered 16,367 officers and men comprising 198 line companies distributed among 4 artillery regiments, 5 mounted regiments, and 10 regiments of infantry. Out of that, a number went to the Confederate side. The Union Army quickly grew to over 2 million men. They pretty-much had no choice but to promote any regular officers they had to senior command.
At the start of WW-I, it was a similar deal, with a force of 90,000 being quickly expanded to over 4 million.
If what we're talking about in this new Star Trek universe is a situation where they just began a war with the Romulans where 95% the Fleet consists of people who had been raw civilians a few months prior, then yes they would have no choice except to use whatever regular officers that they had available. I guess I'll find the background when I go see it later this week.
"HERE'S TO SICKLY SEASONS AND BLOODY WARS." - Famous British toast.
"sickly seasons and bloody wars" were the circumstances where promotion from Midshipman to Captain did take 20 years.
In peacetime 75% of Lieutenants, 80% of Commanders, and 90% of captains were unemployed on half pay, and noöne was being promoted, for any reason.
Super Rapid promotion only occurs during extended major wars, not as a reward (that's what medals are for). And all the back story of the Federation says the this was not a time of extended total wars. (For one thing Starfleet is a lameass military clearly showing the effects of peacetime neglect)