Current way of recruiting mercenary soldiers through UI looks like this:
As you would agree current implementation is not on par with quality of UI in rest of the game has. You can't see the soldier you are recruiting and you can't get any info about it without typing to the encyclopedia which is a hassle. Since the button is not appealing, players tend to not use this feature. Even misclicking while trying to sell prisoners is possible.
I have 2 different solutions to this problem that I have tried to illustrate poorly but you should get the idea.
1) Recruit mercenaries through general recruitment menu
First of all you can see who you are recruiting this way and if you want more information about him you can simply right click to get his encyclopedia page. You would be able see campaign speed and wage changes too. You can also select how many you want recruit this way and I don't think this qualifies as a balance change because if you are low on funds or don't have enough space for all of them, game lets you recruit less.
This might require some changes regarding to the how this screen works to be able to support high number of mercenaries but you would now this better.
2) Recruit them through tavern UI character portraits
If first solution doesn't fit your agenda then consider this one. At least we would be able to see who we are recruiting and we can simply right click to get more info this way. Always putting mercenaries at first place in the UI should make them more easily accessible in a case of too many wanderers.
As you would agree current implementation is not on par with quality of UI in rest of the game has. You can't see the soldier you are recruiting and you can't get any info about it without typing to the encyclopedia which is a hassle. Since the button is not appealing, players tend to not use this feature. Even misclicking while trying to sell prisoners is possible.
I have 2 different solutions to this problem that I have tried to illustrate poorly but you should get the idea.
1) Recruit mercenaries through general recruitment menu
First of all you can see who you are recruiting this way and if you want more information about him you can simply right click to get his encyclopedia page. You would be able see campaign speed and wage changes too. You can also select how many you want recruit this way and I don't think this qualifies as a balance change because if you are low on funds or don't have enough space for all of them, game lets you recruit less.
This might require some changes regarding to the how this screen works to be able to support high number of mercenaries but you would now this better.
2) Recruit them through tavern UI character portraits
If first solution doesn't fit your agenda then consider this one. At least we would be able to see who we are recruiting and we can simply right click to get more info this way. Always putting mercenaries at first place in the UI should make them more easily accessible in a case of too many wanderers.