I tried all kinds of leather cleaners on my seats. They were far better than yours at their dirtiest. NONE of the leather cleaners did anything noticeable. They removed maybe 5% of the dirt.
After a good amount of detailing advice research I found that most any pro detailers think the off the shelf leather cleaners are a joke. They suggested using an all purpose cleaner like this:
Amazon.com: Meguiar's D10101 Detailer All Purpose Cleaner 1 Gallon: Automotive
I bought that stuff and a leather cleaning brush:
Amazon.com: Chemical Guys ACC_S95 Long Bristle Horse Hair Leather Cleaning Brush, , 1 Pack: Automotive
I also bought these so I have a diluted bottle of 4:1, 10:1 and straight water.
Amazon.com: Chemical Guys ACC_121.16HD-3PK Chemical Resistant Heavy Duty Bottle and Sprayer (16 oz) (Pack of 3): Automotive
I cannot stress how nice this setup has been. It cleans more than 10x as well as the off the shelf leather cleaners and I only use the 10:1 dilution on leather. The downside is that it is harsher, even at 10:1, and requires you to rinse immediately and condition immediately. The end result is astounding though. My seats look nearly new now.
Sorry if I sound like an infomercial, but it's been a night and day difference for me. I was so frustrated with the Leatherique and Lexol type cleaners that I just gave up for a couple years. Now that I have that McGuiars 101 stuff, I use it on everything and it's fantastic. I'm sure any other detailing all purpose cleaner would do the trick as well with a good brush.
Be careful with the brushes as some are labeled as upholstery brushes, but they are way too stiff and will ruin leather and the stitching.
Good luck! I bet with the right cleaners you can get that leather looking new again.
-Andy