I would agree with you if speaking of the aerator at the faucet as the cold and hot both flow through the same part! Not sure of what other filter would be in the line to effect only the hot water.
My thought would be that the cartridge inside the faucet is at fault. Assuming the faucet is as built and not changed at some point?
Parts drawings here for the whole picture!
https://catalog.winnebagoind.com/menu/Parts.htm
Click these snips for what I see as the problem!
Still looks like this faucet?
The part numbers if shopping at any big box store? This is assuming they have not done something like change model numbers, etc., so approach with care!!
I never trust until it works!
A part blowup to see what I think has happened.
Way down in the faucet there is a cartridge of metal and plastic. The metal handle is poured/made in the plastic of the cartridge ball. Normally the metal move forward/back to turn water on. But it has to turn left/ right to choose hot or cold. The metal can break loose from the plastic in a way that lets it still move to on or off. But it can be loose to turn the metal and not move the plastic. So I think you are stuck with the plastic part that moves from cold flow to hot flow being left with just a tiny mix of hot in a lot of cold and moving the handle doesn't move the plastic!
Kind of guessing but a look at a store on the cartridge may let it make more sense!
I numbered the steps but getting some of it to break loose can takes some fuss as the minerals tend to stick them together! A little fuss and hold your mouth just right, may help??
Not usually hard but just fussy at times. Do Turn off the water FIRST!
Link to new design cartridge which looks like it might be less plastic and last better? Also some videos that may make it more clear than "word salads"!
https://www.homedepot.com/p/MOEN-Dur...440559#overlay