I don't think seasons do anything--I've had the same tax rate "same peasants complaining" for several IG years now.
What you need to understand is the number of knights you have increases the efficiency of the region. Let me use Raviel as a real-life example.
Right now, my townsland has 2 estates, each using 50% of the land. Their efficiency is only 72%. If i had 4 estates, each with 25% of the land, then their efficiency would be 100%. The most efficient size varies per region.
My estate collects 231 gold right now. Shrinking it to 25% would decrease my tax to 159--so a 50% decrease in estate had only a 31% decrease in gold income, not a terrible trade. Besides, I would be getting more gold from the 3 knights, so instead of about 60 gold lord's share--for a lords share of 25% on the 50% estate--I would be getting 120 gold from my knights. 120 lords share + 159 lords estate=279, which means that my income would actually be higher with a smaller estate! Plus, the region as a whole would go from 462 gold collected, to 641 collected.