In real life, medieval armies were largely levies. High level armor and weapons weren't affordable or accessible to anyone who wasn't noble and wealthy especially since Europe didn't field standing armies until late into the Hundred Years War that the French started fielding a standing army. Prior to that, medieval armies were raised from levies with a small percentage of the army being nobility and well armed/armored retainers. And atop that, medieval armies were VERY expensive in upkeep - for instance it was Edward I's defaulting on loans from Italian bankers that created the term "bankruptcy" (breaking the benches(banks)) in funding his wars with Wales and Scotland. Leveling up tiers should be very prohibitively expensive especially past Tier 3. This is important since archery has been heavily nerfed in mods because it's basically overpowered in vanilla and relies on levy heavy armies to be even effective. (i.e. Khuzaits) even though historically the Mongols were nearly unbeatable in battles - it took the death of a Khan and the kulturai afterwards recalling the Mongol leaders to attend it to halt a planned invasion of all of Western Europe in it's track as well as later splitting the Mongol Empire into four different kingdoms - the IIkhanate, the Golden Horde, the Changatai and the Yuan Hordes.
There's a lot of misconceptions in this post. I will correct them based on the small, but relevant reading I've done on the subject.
Bannerlord is based on the 600-1000 time period. In that time period, levied soldiers were mainly used for
self-defense in their local area, rather than general travelling around with the lord all over the place all year round (which would have been very impractical for farmers who had crops to tend to back home!). When it came to offensive armies that travelled around with the lord like in Bannerlord to invade new territory and make raids, it was professional soldiers. The Frankish warlords in Western Europe fielded warbands called the
comitatus who were dedicated warriors, often fairly well-equipped cavalrymen, who went out on raids while the levies were only occasionally used in invading armies. If you look at the Norman conquests of Italy, you will read about armies of just professional soldiers and mercenaries conducting the invasions. Another example from Anglo-Saxon England is the Fyrd: "It was the responsibility of the shire fyrd to deal with local raids. The king could call up the national militia to defend the kingdom, however in the case of hit and run raids, particularly by Vikings, problems with communication and raising supplies meant that the national militia could not be mustered quickly enough, so it was rarely summoned." In short, I think the militia who appear when you raid villages already properly represents the main real-life role of peasant levies.
Regarding equipment, quality equipment that T4 troops wield in Bannerlord, such as mail armor, was not by totally "inaccessible" for people in the "middle class" of Frankish society. The Lex Ribuaria, the manuscripts which laid out the legal code of the Franks, state the value of a shield and spear at 2 solidi. A mail tunic was worth 12 solidi. For comparison, the fine for a slave seducing a maidservant at that time was 3 solidi (while the fine for a freeman was 15 solidi). If even slaves could theoretically be expected to own 3 solidi to pay a fine, then your average person on a soldier's wage could probably muster up 12 solidi at some point in their lives as a one-time investment! So I don't think leveling past T3 should be prohibitively expensive.
The Mongols were not nearly unbeatable in battles, and did suffer multiple defeats. It's a common misconception that the planned invasion was caused by the death of the Khan, when this is unsure and very unlikely.
In fact, the message of the Khan's death wouldn't have even had time to reach them by the time they had already given up and left, and the Mongol forces were not aware the Khan had died, according to historians writing at that time. Further invasions of Europe were called off because after the
disastrous failures of
the third and second invasions of Poland and Hungary, much of Eastern Europe had learned that stone castles, trained crossbowmen, and heavily armored knights could defeat Mongol armies in battle. The Mongols were stalled on the plains and just waited for a few seasons before deciding to go home.
Another thing to note about the Mongols is that they actually contained a very large heavy cavalry element, roughly a third of the army. Their horse archers would attack and retreat repeatedly to either wear down the enemy or bait them into a charge. Then, the heavy cavalry would make a charge to deal the decisive blow.
TL;DR: If you want to go by history, the game's tier distribution already represents real life pretty well, maybe could do with some small tweaks. I do agree archers are overpowered in vanilla, though this is more due to armor being underpowered and providing too little protection.
