Are you saying that you decide to go besiege places on a whim, without planning ahead for it?
Are you saying that most players plan ahead to the point of considering whether starving out a fortress is the best strategic option based on every single factor in the game's simulation, and then running around getting enough food to feed an army for the entire duration of sitting around doing nothing and having no fun? Every single time they besiege anything?
Secondly, the issue is sieges. Lancers' armor is decent (and skills as well, I suppose) but not nearly as good as the other faction's options.
Lancers' body and head armor is actually
the best in their tier (as far as I've spent time to look).
* T4 Khergit Lancers have a max of 40 head armor, 48 body armor and 13+18 leg armor.
* T4 Swadian Men-At-Arms have 33, 42 and 14+24.
* T4 Rhodok Vet Spearmen have 35, 42 and 14+21.
* T4 Nord Warriors have 30, 37 and 12+16.
* T4 Sarranid Horsemen have 25, 40 and 14+20.
* T4 Vaegir Infantry have 38, 40 and 13+16.
Their armor is obviously worse than T5 Swadian Knights, but the weapons they get are better for sieges.
Lancer's axe swings for 38c, 98 speed, 76 reach, and bonus against shields; and their shield has 250 durability, 22 resist, and 100 speed.
Knight's sword swings for 33c with 96 speed and reach of 105, no shield bonus; and their shield has 220 durability, 23 resist, and 100 speed.
With very basic player micro (f1+f1 then f1+f3, so they don't trickle in gradually), AI set to Good and all damage on Normal:
* 25 Lancers siege assaulting 25 Swadian T3/4 Footmen/Infantry = Lancers win with 5 casualties.
* 25 Lancers siege assaulting 25 Rhodok T4/5 Vet. Spearmen/Sergeants = Lancers win with 14 casualties.
* 25 Lancers siege assaulting 25 Vaegir T4/5 Horsemen/Knights = Horsemen/Knights win with 19 casualties. (for comparison, sending other Horsemen/Knights to do the same thing results in the defenders still winning, with 11 casualties).
* 25 Lancers siege assaulting 19 Swadian T4 Men-at-arms+6 Knights = Lancers win with 14 casualties!
Just to be sure, I swapped it around, did it the same and Lancers won again on defense, with 8 casualties.
I don't think they are that great in field battles either due to some hafted blades vs. full lance in terms of killing power
Like I said, hafted blades beat lances in situations like uneven terrain and village battles. Not every Warband field battle is a flat plain, a lot of them have crazy hills and mountainsides, rivers, etc, and the player can use that to their advantage. Sit your Lancers on a hill so the lance charge is slowed down, and they will beat MAA+Knights. I just did it ingame.
Unfortunately, WB's campaign required you to besiege settlements constantly so any faction that does poorly there is going to perform pretty poorly in player hands.
Then it's a good thing that Lancers are actually not that bad in sieges at all.
At the same time, Sturgia doesn't have those flaws.
Sturgia is just as bad as the Khergits: Minorly weak against the player and in the hands of the player. Its horrible geography which slows army reinforcement time when the player is attacking it (a flaw Khergits don't have as their borders are protected by mountains and cities are clustered together in a triangle), its low potential troop tree when being used by the player or AI, its much weaker cultural bonus compared to the Battanian one the player can pick instead, etc. make it underpowered to the same degree the Khergits are.