After using legends mode for a little bit, I have some suggestions on how to possibly reduce clutter to bearable levels.
Timelines
When turning off all "non-important" events (in other words, displaying only the yellow text), it seems that 90% of the events consist of:
a) Random festivals, and every little detail about them listed individually (so you have stuff like "107th Crossbows Throwing Competition of the Armored Festival began" being regarded as a very important event. No joke, I literally pulled that example straight from the game.)
b) Random rampages and abductions.
These don't really ring the bell for me as being particularly important events for world history. When toggling "important events only", the following things should be displayed:
A) Megabeast deaths
B) Major sites being founded, conquered, or destroyed
C) Civilizations/Religions/Factions being founded or extinguished
D) Particularly 'important' (this might be difficult to determine) people getting into positions of power, e.g. powerful monarchs ascending the throne, extremely adept generals entering service, etc.
E) Wars breaking out and ending, major battles (Note - wars seem to be almost broken currently in worldgen. Basically every border skirmish is treated as a major war by the game, hence the vast majority of the "wars" in legends mode are single-battle affairs that last less than half a year. This should be fixed, obviously)
F) Important artifacts getting created, changing hands, lost or destroyed
Ideally, there should be some granularity when it comes to displaying this info, ranging from "Just give me the barest breakdown of the era" to "Give me an infodump of every minor event that happened during the era".
Regions
These should have the format of:
1) Intro
2) Flora and fauna
3) History overview
4) Points of interest
For example:
"The Infinite Fingers was a mountain chain on the continent of The Absolute Realm.
The flora mainly consisted of cottongrass and hair grass, with little in the way of larger vegetation. The fauna was as typical of mountain regions, with the large population of giant bats and giant bobcats being particularly noteworthy.
In primordial times, the mountains were inhabited only by tribes of kea men. During these times, the mighty roc Famime Fuchsiatulip ruled the region from the skies. In 46, the first dwarven settlers from The Nation of Hammers arrived and built the fortress of Cloisterrag. In 102, Famime Fuchsiatulip was struck down by the dwarf Tosid Trancepaint in the 3rd Ravaging of Cloisterrag by Famime Fuchsiatulip. In 183 Cloisterrag was sacked by elven forces in The Fierce Conflict and made part of the Cerulean Empire. In 202 Cloisterrag was retaken by The Nation of Hammers from The Cerulean Empire.
Points of interest:
Cloisterrag (Fortress) is the largest and oldest inhabited settlement in the region
The Tombs of Glistening (Tomb) is a large and ancient tomb complex near Cloisterrag
The Red Peak (Geographical feature) is the highest peak of the region"
Obviously, if someone desired more detailed info (like in the current version), there would be an option for that as well.
If I have any more ideas for other parts of legends mode, I'll post them.