I think that for as long as I have been here..
I've only once seen anyone fight on horseback, and that was a test.
So given how situational the lance is I think the payoff can be a quite bit bigger considering practically 99.999% of the time it's just an expensive spear and the other 0.001% it's a slightly worse Pole Axe. I feel it's probably fair to make it atleast much better than a Pole Axe when the mounted condition is met.
Possibly the price of the lance would have to go up depending on the modifier when mounted, though keeping in mind mounted combat is rare enough that it does not warrent the same price as weapons with the same modifier by default.
Comparing the Lance to the Pole Axe it's 5mhl buys you an objectively better weapon without the mounted condition and 2 less str.
Lance
Description: Doubles as Spear (ATK 3) when used dismounted Not usuable by Rangers
Strength (STR) Required: 22
Attack Modifier: 5
Equipment Slots Used: 2
Number of Uses: 0 (0 = unlimited)
Two-Handed? Yes
Weapon Class: C
Price: 90.00 Mehrials
Pole Axe
Description: Not usuable by Rangers
Strength (STR) Required: 20
Attack Modifier: 5
Equipment Slots Used: 2
Number of Uses: 0 (0 = unlimited)
Two-Handed? Yes
Weapon Class: C
Price: 95.00 Mehrials