I climbed up the other day and looked at mine. Ten years burning no brushing, old brick chimney. Small amount of light dust at the top layer of bricks you could wipe off with your finger and that's it. Now, I do use that chemical stuff you throw a scoop in, but that's it, and only started doing it last year, just because it is cheap and maybe it works, dunno. Doesn't seem to hurt. I have seen the chimney a bit dirtier with an extremely light oily film before, but it wasn't thick or anything. . The main reason, my opinion, I have no actual data other than observational anecdotal, it stays clean is I refuse to use an exhaust damper, I just have wide variety of species and sizes for firewood and a a controllable air intake that screws in and out. I adjust my burn by what I throw in and how much air it gets, I never restrict the exhaust. It's like, pick a gear and throttle setting to drive. You just learn how, depending on what your needs are at the time.
When I first started burning in a stove, I had a flue damper and dang no matter what I did I got creosote buildup, hot fire or not, and had to clean the pipes. I thought about it some, removed the damper, and never had a lick of trouble since.
OK, eventually I want to add a stainless liner and extend my chimney height a few feet, but that's it. I still don't anticipate any creosote buildup, not anything major at all. It's them dang dampers and burning wet wood, smouldering it, that does it. If you need to top off once a night, meh...I get up anyway for a pitstop and have always been able to fall back asleep fast.