Firstly Starfleet Academy is set centuries after TNG and DS9, at a time when the Federation is trying to rebuild after the devastation of The Burn. The Academy has only just re-opened and started taking new recruits, and with the galaxy still recovering the feed of already accomplished cadets just isn't there.
That said, the TNG version in particular was ridiculous. They apparently traumatized cadets as much as possible to see if they were worthy of joining. Aside from not every cadet having the same traumatic experiences to draw on, that's just cruel and ignores the fact that the whole point of the academy is to prepare students for that kind of thing.
In SA the cadets are expected to be at the top of their game... Once they have been taught how to do that. We see them improving throughout the first season, until they are finally able to work well as a crew (under the leadership and supervision of Reno and other officers). Of course there is also an emotional and coming of age journey there, because that's what happens to young adults. Most Western militaries are aware of this and cater for it, as do universities.
Ake left Starfleet because she saw what it had become because of The Burn, and didn't like it. She accepts that was a mistake, and she should have tried harder to put it right instead of walking away. That's a great story and the reason she was chosen to lead the Academy - she both remembers Starfleet before The Burn from her long lifespan, and is strongly motivated to make sure the next generation of officers learn from her mistakes. That's also why she wants to recruit Caleb.
The rest is just because it's a TV show. We aren't there to watch lectures, and most of what they teach is made up pseudo-science anyway. Learning how to operate an imaginary starship that works however the writers say it does isn't very interesting for the audience. It's the same with the cadets getting into so much danger (and they do use the holodeck extensively when possible) - it's like how for some reason the various Enterprises we have seen over three seasons get into highly improbable situations literally every other week. On TNG they have families aboard, but regularly end up with the ship and everyone's lives on the line.
That's how TV works. Real life is repetitive and boring, so TV doesn't try to be realistic.