My core inspiration for the mechanics the AD&D training rules, and most of the time it is not more complicated than that; when it is time to level, you expend the requisite cash, and you are presumed to have learned what you need to learn. It is only if you want to learn the Dance of Blades that you need to go questing for it.
"Training montage" is not what I am going for. I had a DM once who made us roleplay the entire of the training process, rather than having it occur during downtime. It was painful.
Knowing what options are available when it comes time for training is not an issue for the common classes, like fighter and rogue. I make options regionally based, so they will likely have already been fighting NPCs trained in the regional style. Coming up with those styles is not a chore because (a) I like the worldbuilding, it is part of the reason I am a DM; and (b) without going into a lot of explanation as to how it works, 4e already has themes it is possible to identify and build around.
Which brings me to
@squeen's point. I didn't expect WotC to generate all this, but they did. What baffles me is that, having generated this content, why do they then discouraging DMs from using it?
I would also point out that, as with the 1e DMG, this content
implies a setting, it does not
impose a setting. Just like AD&D implies a setting by the description of its monsters, the spells available, the content of random encounter lists, the treasure tables, etc. Interpreting those implications and incorporating them into your campaign is up to you. It is a restriction that helps inspire, the same way people use random tables. Note I probably wouldn't be able to do this efficiently, except that all of the options are digitized and searchable.
Say I want to generate a combat style for a human barbarian tribe, and I decide that their primary weapon of war is the spear. There are 8 different combat styles that use spears, so I pick one more or less randomly. Hunting Spear style uses any kind of spear, focuses on athletics, and gives damage bonuses for attacks on large creatures; it also has a list of combat maneuvers that, while not mandatory, are modified by the style. Fighters, rangers (which in 4e are less mystical nature warriors and more skirmishing fighters), and warlords (a variant "leader" type of fighter) can use the style; rogues cannot. All of the associated maneuvers are melee attacks, not ranged attacks, so that tells me something about how they wage war and probably how they hunt. The fact that they do more damage to large creatures may indicate the kind of prey they go after, maybe mastadons, and/or there might be a tribe of ettins nearby. Since no specialized spear is specified they probably use a variety of spears, likely including javalins even though thrown weapons is clearly not their forte.
The list of ranger maneuvers includes maneuvers that can only be used by beastmaster rangers. I hadn't really thought about this being a tribe that keeps pets, but now I decide they have long been allied with a wolf pack. Beastmaster's aren't the strongest type of ranger; I will think about what that means in terms of the tribe's priorities.
There are going to be some gaps in the list of options, so I think about how I want to fill it. Do I focus on options relating to spears, or options relating to humans, or options relating to fighters? I pick one and fill out the list.
Now I look at what options have been selected and make an assessment as to how many of them are good options, and haw many are bad options. And I think about what that says about the tribe, and what they value. Are their strengths in their fighters, or their rangers, or their leaders, and why? Since the three classes would obviously be trained separately, I make three warrior septs or factions in the tribe, and think about what their major areas of responsibility would be, and how they would interact.
Now I want to create a spiritual leader, and maybe an elite warrior to two. The Sentinel Druid has an option for a wolf beast companion, so I go with that. Sentinels are not particularly good fighters, and can't shapeshift like other druids, but they are stronger healers; this tells me something about what the tribe values; this isn't a tribe of reavers, they are a kinder, gentler people, likely with a strong gathering tradition in addition to hunting, and a real "work with nature" approach to both. Going with the wolf theme, I see there are a few barbarian options that are wolf-flavoured, so I make an elite spear-using barbarian character based on those options, and the non-class specific options that I picked for the fighter types. I also pick the less aggressive options for the barbarian; one of those revolves around the barbarian's war cry. I like the idea of howling wolves, and communicating with wolves, so I add the warcry to their warrior culture.
So now I have a tribe of hunters and gatherers who have a close relationship with a wolf pack. They live in harmony with nature, and respect those who embody that connection at least as much as their best hunters. They kill for food, not for sport or for loot, and they take only what they need. Their preferred weapon is the spear with which they kill their prey; ranged javelins are used to drive very large game into a killing zone populated by heavy spear wielders. They war often enough with a nearby tribe of ettins that they have developed specialized tactics for dealing with them. Their war cry, and the way they signal each other in battle, is based on the howls and baying of wolves. Their spiritual leaders are druids, and their elite warriors are those who can channel the spirit of the wolf.